Correcting typing issue and whitespace

Removed double-space and adding a False return indicating that the event has not been handled.

nion/ui/QtUserInterface.py

@@ -1662,7 +1662,8 @@ def mousePressed(self, x: int, y: int, raw_modifiers: int) -> None:
     def mouseReleased(self, x: int, y: int, raw_modifiers: int) -> bool:
         self._register_ui_activity()
         if callable(self.on_mouse_released):
-            return  self.on_mouse_released(x, y, QtKeyboardModifiers(raw_modifiers))
+            return self.on_mouse_released(x, y, QtKeyboardModifiers(raw_modifiers)
+        return False
 
     def mousePositionChanged(self, x: int, y: int, raw_modifiers: int) -> None:
         if callable(self.on_mouse_position_changed):