Avoid possible exception when toggling full-screen

In `examples/user_interfaces/embedding_in_tk.py`, a FigureCanvasTkAgg is embedded into a Tkinter window and the default mpl key bindings are implemented with matplotlib.backend_bases.key_press_handler. If the user attempts to toggle full-screen mode by pressing 'f', an AttributeError is raised because the FigureCanvasTkAgg has no 'manager' attribute. Indeed, since pyplot is not being used, no FigureManagerTkAgg object gets created. One fix is to check for the 'manager' attribute and do nothing if it doesn't exist. (This is what is done in FigureCanvasBase.get_window_title/set_window_title, for example.)
matplotlib · tacaswell · Aug 6, 2015 · Aug 1, 2015 · Aug 1, 2015 · Aug 1, 2015
commit ee16b6cce5cf2b7a012c98b7cb7535d178717295
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2479,7 +2479,8 @@ def key_press_handler(event, canvas, toolbar=None):
 
     # toggle fullscreen mode (default key 'f')
     if event.key in fullscreen_keys:
-        canvas.manager.full_screen_toggle()
+        if hasattr(canvas, 'manager'):
+            canvas.manager.full_screen_toggle()
 
     # quit the figure (defaut key 'ctrl+w')
     if event.key in quit_keys: