Mark session with unsaved changes when current selection is grouped.

This was an oversight in the recent grouping functionality (introduced
in e162fbe), where it was overlooked to invalidate the document
after the select was moved into a new group.

Source/GUI/MemWatcher/MemWatchWidget.cpp

@@ -312,7 +312,13 @@ void MemWatchWidget::setSelectedWatchesBase(MemWatchEntry* entry, Common::MemBas
 
 void MemWatchWidget::groupCurrentSelection()
 {
-  m_watchModel->groupSelection(simplifySelection());
+  const QModelIndexList indexes{simplifySelection()};
+  if (indexes.isEmpty())
+    return;
+
+  m_watchModel->groupSelection(indexes);
+
+  m_hasUnsavedChanges = true;
 }
 
 void MemWatchWidget::cutSelectedWatchesToClipBoard()