FIX: be more cautious about checking widget size

This can fail if the c++ side of the object has already been cleaned up
but the Python side is still lingering (due to refs in callbacks).

closes matplotlib#29618

Author: tacaswell

lib/matplotlib/backends/backend_qt.py

@@ -517,7 +517,7 @@ def _draw_idle(self):
             if not self._draw_pending:
                 return
             self._draw_pending = False
-            if self.height() <= 0 or self.width() <= 0:
+            if _isdeleted(self) or self.height() <= 0 or self.width() <= 0:
                 return
             try:
                 self.draw()