Refix check for manager presence in deprecated blocking_input.

The whole module has been deprecated as the library is now using
_blocking_input, which does not have the same problem, but it still
seems better to fix this typo asap.

Author: anntzer

lib/matplotlib/blocking_input.py

@@ -83,7 +83,7 @@ def __call__(self, n=1, timeout=30):
         self.n = n
         self.events = []
 
-        if self.figure.canvas.manager:
+        if self.fig.canvas.manager:
             # Ensure that the figure is shown, if we are managing it.
             self.fig.show()
         # Connect the events to the on_event function call.