Update _base.py

Author: ZzN1NJ4

lib/matplotlib/axes/_base.py

@@ -1680,6 +1680,8 @@ def set_aspect(self, aspect, adjustable=None, anchor=None, share=False):
             aspect = 1
         if not cbook._str_equal(aspect, 'auto'):
             aspect = float(aspect)  # raise ValueError if necessary
+            if aspect<0:
+                raise ValueError("aspect must be positive")
 
         if share:
             axes = {sibling for name in self._axis_names