fix in RectSelector

samples/python2/common.py

@@ -139,10 +139,11 @@ class RectSelector:
                 if x1-x0 > 0 and y1-y0 > 0:
                     self.drag_rect = (x0, y0, x1, y1)
             else:
-                if self.drag_rect:
-                    self.callback(self.drag_rect)
+                rect = self.drag_rect
                 self.drag_start = None
                 self.drag_rect = None
+                if rect:
+                    self.callback(rect)
     def draw(self, vis):
         if not self.drag_rect:
             return