QPainter: Avoid leaking memory on unbalanced save/restore

If a QPainter ended without all saved states having been restored, the
state stack would leak memory.

Fixes: QTBUG-77843
Change-Id: I760904d6391de24a4867be54fa1bebf76be14ba7
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/gui/painting/qpainter.cpp

@@ -1710,8 +1710,8 @@ void QPainter::restore()
 
 static inline void qt_cleanup_painter_state(QPainterPrivate *d)
 {
+    qDeleteAll(d->states);
     d->states.clear();
-    delete d->state;
     d->state = 0;
     d->engine = 0;
     d->device = 0;