UI: Restore theme if settings window exit with [x]

Fixes a bug where if the theme was changed, then wasn't saved, and the
user exits the window with the [x] button, then chooses "No" when asked
to save settings, it would not restore the original theme.

UI/window-basic-settings.cpp

@@ -3560,6 +3560,9 @@ bool OBSBasicSettings::QueryChanges()
 	} else if (button == QMessageBox::Yes) {
 		SaveSettings();
 	} else {
+		if (savedTheme != App()->GetTheme())
+			App()->SetTheme(savedTheme);
+
 		LoadSettings(true);
 #ifdef _WIN32
 		if (toggleAero)