Merge pull request #7 from Galland/master

Bugfix releasing a key that was pressed over another window (i.e. Shift)

Author: fdb

nodebox/graphics/context.py

@@ -3811,7 +3811,10 @@ def _on_key_release(self, keycode, modifiers):
             layer.on_key_release(self.key)
         self.on_key_release(self.key)
         self._keys.char = ""
-        self._keys.remove(keycode)
+        try:
+            self._keys.remove(keycode)
+        except ValueError:
+            pass
         self._keys.pressed = False
 
     def _on_text(self, text):