tk: Skip setting cursor if window is unavailable.

QuLogic · QuLogic · commit c2e50112b931 · 2020-05-12T18:56:34.000-04:00
This is really optional, and fails in `Figure.savefig` if `plt.show()`
is called before it.
diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
@@ -541,8 +541,12 @@ def release_zoom(self, event):
 
     def set_cursor(self, cursor):
         window = self.canvas.get_tk_widget().master
-        window.configure(cursor=cursord[cursor])
-        window.update_idletasks()
+        try:
+            window.configure(cursor=cursord[cursor])
+        except tkinter.TclError:
+            pass
+        else:
+            window.update_idletasks()
 
     def _Button(self, text, image_file, toggle, command):
         image = (tk.PhotoImage(master=self, file=image_file)
