Fix pan/zoom crashing when widget lock is unavailable (matplotlib#23373)

* Fix pan/zoom crashing when widget lock is unavailable

* Add test for pre-locked zoom/pan

Author: kianelbo

lib/matplotlib/backend_bases.py

@@ -3043,6 +3043,9 @@ def pan(self, *args):
 
         Pan with left button, zoom with right.
         """
+        if not self.canvas.widgetlock.available(self):
+            self.set_message("pan unavailable")
+            return
         if self.mode == _Mode.PAN:
             self.mode = _Mode.NONE
             self.canvas.widgetlock.release(self)
@@ -3095,6 +3098,9 @@ def release_pan(self, event):
         self.push_current()
 
     def zoom(self, *args):
+        if not self.canvas.widgetlock.available(self):
+            self.set_message("zoom unavailable")
+            return
         """Toggle zoom to rect mode."""
         if self.mode == _Mode.ZOOM:
             self.mode = _Mode.NONE

lib/matplotlib/tests/test_backend_bases.py

@@ -175,6 +175,17 @@ def test_interactive_zoom():
     assert not ax.get_autoscalex_on() and not ax.get_autoscaley_on()
 
 
+def test_widgetlock_zoompan():
+    fig, ax = plt.subplots()
+    ax.plot([0, 1], [0, 1])
+    fig.canvas.widgetlock(ax)
+    tb = NavigationToolbar2(fig.canvas)
+    tb.zoom()
+    assert ax.get_navigate_mode() is None
+    tb.pan()
+    assert ax.get_navigate_mode() is None
+
+
 @pytest.mark.parametrize("plot_func", ["imshow", "contourf"])
 @pytest.mark.parametrize("orientation", ["vertical", "horizontal"])
 @pytest.mark.parametrize("tool,button,expected",