Fix some QPointers not clearing promptly in Qt5

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project somewhat adheres to [Semantic Versioning](https://semver.org/sp
    - Previously, the middle mouse button could be used as a shortcut with the pencil tool to switch to bucket-fill mode. This is now achieved using the `Alt` key.
 
 ### Fixed
+- Fix crash on older versions of Qt when reopening a project with certain windows open.
 - Fix potential crash when painting and the cursor leaves the map area.
 - Fix rare crash while quitting Porymap.
 - Fix `Edit > Clear Map Entries` in the Region Map Editor not saving the applied changes.

src/mainwindow.cpp

@@ -3246,7 +3246,7 @@ bool MainWindow::closeSupplementaryWindows() {
     // We have some QPointers to windows that may have been closed above.
     // Make sure we force them to update to nullptr now; they may be read
     // before the next event loop gets a chance to update them.
-    QApplication::sendPostedEvents();
+    QApplication::sendPostedEvents(nullptr, QEvent::DeferredDelete);
     return true;
 }