FIX: also account for itertools.count used in _AxesStack

Author: tacaswell

lib/matplotlib/figure.py

@@ -105,6 +105,17 @@ def current(self):
         """Return the active axes, or None if the stack is empty."""
         return max(self._axes, key=self._axes.__getitem__, default=None)
 
+    def __getstate__(self):
+        return {
+            **vars(self),
+            "_counter": max(self._axes.values(), default=0)
+        }
+
+    def __setstate__(self, state):
+        next_counter = state.pop('_counter')
+        vars(self).update(state)
+        self._counter = itertools.count(next_counter)
+
 
 class SubplotParams:
     """