UI: Reset duration when removing show/hide transition

UI/window-basic-main-transitions.cpp

@@ -1184,6 +1184,8 @@ QMenu *OBSBasic::CreateVisibilityTransitionMenu(bool visible)
 		if (id.isNull() || id.isEmpty()) {
 			obs_sceneitem_set_transition(sceneItem, visible,
 						     nullptr);
+			obs_sceneitem_set_transition_duration(sceneItem,
+							      visible, 0);
 		} else {
 			OBSSource tr = obs_sceneitem_get_transition(sceneItem,
 								    visible);