Release mouse grabs when owning Axes is removed

Otherwise, _nothing_ will remove the grab, and no other Axes can grab
the mouse (either raising the `RuntimeError` exception, or in the case
of widgets, ignoring mouse events altogether.)

Fixes matplotlib#25345

Author: QuLogic

lib/matplotlib/figure.py

@@ -931,6 +931,7 @@ def _break_share_link(ax, grouper):
         self._axobservers.process("_axes_change_event", self)
         self.stale = True
         self._localaxes.remove(ax)
+        self.canvas.release_mouse(ax)
 
         # Break link between any shared axes
         for name in ax._axis_names:

lib/matplotlib/tests/test_backend_bases.py

@@ -95,6 +95,16 @@ def test_non_gui_warning(monkeypatch):
                 in str(rec[0].message))
 
 
+def test_grab_clear():
+    fig, ax = plt.subplots()
+
+    fig.canvas.grab_mouse(ax)
+    assert fig.canvas.mouse_grabber == ax
+
+    fig.clear()
+    assert fig.canvas.mouse_grabber is None
+
+
 @pytest.mark.parametrize(
     "x, y", [(42, 24), (None, 42), (None, None), (200, 100.01), (205.75, 2.0)])
 def test_location_event_position(x, y):