workbook: Throw if index in (const) sheet_by_index is out of range

The documentation of (const) sheet_by_index already mentions that
invalid_parameter exception will be thrown if the index is out of
range, but the implementation was missing.

source/workbook/workbook.cpp

@@ -681,6 +681,11 @@ worksheet workbook::sheet_by_index(std::size_t index)
 
 const worksheet workbook::sheet_by_index(std::size_t index) const
 {
+    if (index >= d_->worksheets_.size())
+    {
+        throw invalid_parameter();
+    }
+
     auto iter = d_->worksheets_.begin();
 
     for (std::size_t i = 0; i < index; ++i, ++iter)

tests/workbook/workbook_test_suite.cpp

@@ -49,6 +49,8 @@ public:
         register_test(test_add_sheet_at_index);
         register_test(test_get_sheet_by_title);
         register_test(test_get_sheet_by_title_const);
+        register_test(test_get_sheet_by_index);
+        register_test(test_get_sheet_by_index_const);
         register_test(test_index_operator);
         register_test(test_contains);
         register_test(test_iter);
@@ -151,6 +153,23 @@ public:
         xlnt_assert_equals(new_sheet, found_sheet);
     }
 
+    void test_get_sheet_by_index()
+    {
+        xlnt::workbook wb;
+        auto new_sheet = wb.create_sheet();
+        xlnt_assert_equals(new_sheet, wb.sheet_by_index(1)); // in range
+        xlnt_assert_throws(wb.sheet_by_index(2), xlnt::invalid_parameter); // out of range
+    }
+
+    void test_get_sheet_by_index_const()
+    {
+        xlnt::workbook wb;
+        auto new_sheet = wb.create_sheet();
+        const auto &wb_const = wb;
+        xlnt_assert_equals(new_sheet, wb_const.sheet_by_index(1)); // in range
+        xlnt_assert_throws(wb_const.sheet_by_index(2), xlnt::invalid_parameter); // out of range
+    }
+
     void test_index_operator() // test_getitem
     {
         xlnt::workbook wb;