Fix threading issue with startup pw popup

The GUI is slow to update after accepting a password, but a cursory ten minute investigation didn't yield why
I inserted a processEvents() call before ready = true; at the end of Core::start, but that didn't help.
Define the total time between the password dialog disappearing and the UI updating with your own status is T:
Then my debug statement indicated that this processEvents call happened around 1/3T, raising two questions:
1) What the hell is happening between 0 and 1/3 T? Decryption doesn't take that long...
Note that bad passwords are immediately rejected with a new dialog, so I highly doubt it's the decryption cpu time
2) The remaining 2/3rds: processEvents has been called after the avatar and username signals, yet they
don't update in the UI till time T when everything updates after bootstrapping...

Oh well, like I said, only a cursory investigation

src/coreencryption.cpp

@@ -133,7 +133,7 @@ bool Core::loadEncryptedSave(QByteArray& data)
         Widget::getInstance()->showWarningMsgBox(tr("Encryption error"), tr("The .tox file is encrypted, but encryption was not checked, continuing regardless."));
 
     int error = -1;
-    QString a(tr("Please enter the password for this profile:", "used in load() when no pw is already set"));
+    QString a(tr("Please enter the password for this profile.", "used in load() when no pw is already set"));
     QString b(tr("The previous password is incorrect; please try again:", "used on retries in load()"));
     QString dialogtxt;
 
@@ -152,30 +152,18 @@ bool Core::loadEncryptedSave(QByteArray& data)
 
     uint8_t salt[tox_pass_salt_length()];
     tox_get_salt(reinterpret_cast<uint8_t *>(data.data()), salt);
-    QInputDialog dialog;
-    dialog.moveToThread(qApp->thread());
-    dialog.setOkButtonText(tr("Set password"));
-    dialog.setCancelButtonText(tr("Change profile"));
-    dialog.setWindowTitle(tr("Enter your password"));
-    dialog.setInputMode(QInputDialog::TextInput);
-    dialog.setTextEchoMode(QLineEdit::Password);
+
     do
     {
-        dialog.setTextValue(QString());
-        dialog.setLabelText(dialogtxt);
+        QString pw = Widget::getInstance()->passwordDialog(tr("Change profile"), dialogtxt);
 
-        int val = dialog.exec();
-
-        if (val == QDialog::Accepted)
-        {
-            QString pw = dialog.textValue();
-            setPassword(pw, ptMain, salt);
-        }
-        else
+        if (pw.isEmpty())
         {
             clearPassword(ptMain);
             return false;
         }
+        else
+            setPassword(pw, ptMain, salt);
 
         error = tox_encrypted_key_load(tox, reinterpret_cast<uint8_t *>(data.data()), data.size(), pwsaltedkeys[ptMain]);
         dialogtxt = a + " " + b;
@@ -210,33 +198,20 @@ void Core::checkEncryptedHistory()
     else
         dialogtxt = a;
 
-    QInputDialog dialog;
-    dialog.moveToThread(qApp->thread());
-    dialog.setOkButtonText(tr("Set password"));
-    dialog.setCancelButtonText(tr("Disable history"));
-    dialog.setWindowTitle(tr("Enter your password"));
-    dialog.setInputMode(QInputDialog::TextInput);
-    dialog.setTextEchoMode(QLineEdit::Password);
     bool error = true;
     do
     {
-        dialog.setLabelText(dialogtxt);
-        dialog.setTextValue(QString());
+        QString pw = Widget::getInstance()->passwordDialog(tr("Disable history"), dialogtxt);
 
-        int val = dialog.exec();
-
-        if (val == QDialog::Accepted)
-        {
-            QString pw = dialog.textValue();
-            setPassword(pw, ptHistory, reinterpret_cast<uint8_t*>(salt.data()));
-        }
-        else
+        if (pw.isEmpty())
         {
             clearPassword(ptHistory);
             Settings::getInstance().setEncryptLogs(false);
             Settings::getInstance().setEnableLogging(false);
             return;
         }
+        else
+            setPassword(pw, ptHistory, reinterpret_cast<uint8_t*>(salt.data()));
 
         error = !HistoryKeeper::checkPassword();
         dialogtxt = a + " " + b;

src/widget/widget.cpp

@@ -1236,6 +1236,34 @@ bool Widget::askMsgboxQuestion(const QString& title, const QString& msg)
     }
 }
 
+QString Widget::passwordDialog(const QString& cancel, const QString& body)
+{
+    // We can only display widgets from the GUI thread
+    if (QThread::currentThread() != qApp->thread())
+    {
+        QString ret;
+        QMetaObject::invokeMethod(this, "passwordDialog", Qt::BlockingQueuedConnection,
+                                  Q_RETURN_ARG(QString, ret),
+                                  Q_ARG(const QString&, cancel), Q_ARG(const QString&, body));
+        return ret;
+    }
+    else
+    {
+        QString ret;
+        QInputDialog dialog;
+        dialog.setWindowTitle(tr("Enter your password"));
+        dialog.setOkButtonText(tr("Set password"));
+        dialog.setCancelButtonText(cancel);
+        dialog.setInputMode(QInputDialog::TextInput);
+        dialog.setTextEchoMode(QLineEdit::Password);
+        dialog.setLabelText(body);
+        int val = dialog.exec();
+        if (val == QDialog::Accepted)
+            ret = dialog.textValue();
+        return ret;
+    }
+}
+
 void Widget::clearAllReceipts()
 {
     QList<Friend*> frnds = FriendList::getAllFriends();

src/widget/widget.h

@@ -68,6 +68,8 @@ public:
                                               QMessageBox::StandardButtons buttonss = QMessageBox::Ok);
     Q_INVOKABLE void setEnabledThreadsafe(bool enabled);
     Q_INVOKABLE bool askMsgboxQuestion(const QString& title, const QString& msg);
+    Q_INVOKABLE QString passwordDialog(const QString& cancel, const QString& body);
+    // hooray for threading hacks
     ~Widget();
 
     virtual void closeEvent(QCloseEvent *event);