Drop mouseover when mouse not in the window

Not that this is critical, but it makes behavior of GUI and 2D/3D picking consistent among them.

This also contributes to dropping GUI focus when the mouse leaves the window (in addition to when it loses focus).

scene/main/viewport.cpp

@@ -659,7 +659,11 @@ void Viewport::_notification(int p_what) {
 			}
 
 		} break;
+		case SceneTree::NOTIFICATION_WM_MOUSE_EXIT:
 		case SceneTree::NOTIFICATION_WM_FOCUS_OUT: {
+
+			_drop_physics_mouseover();
+
 			if (gui.mouse_focus) {
 				//if mouse is being pressed, send a release event
 				_drop_mouse_focus();
@@ -2561,6 +2565,31 @@ void Viewport::_drop_mouse_focus() {
 	}
 }
 
+void Viewport::_drop_physics_mouseover() {
+
+	physics_has_last_mousepos = false;
+
+	while (physics_2d_mouseover.size()) {
+		Object *o = ObjectDB::get_instance(physics_2d_mouseover.front()->key());
+		if (o) {
+			CollisionObject2D *co = Object::cast_to<CollisionObject2D>(o);
+			co->_mouse_exit();
+		}
+		physics_2d_mouseover.erase(physics_2d_mouseover.front());
+	}
+
+#ifndef _3D_DISABLED
+	if (physics_object_over) {
+		CollisionObject *co = Object::cast_to<CollisionObject>(ObjectDB::get_instance(physics_object_over));
+		if (co) {
+			co->_mouse_exit();
+		}
+	}
+
+	physics_object_over = physics_object_capture = 0;
+#endif
+}
+
 List<Control *>::Element *Viewport::_gui_show_modal(Control *p_control) {
 
 	gui.modal_stack.push_back(p_control);

scene/main/viewport.h

@@ -383,6 +383,7 @@ private:
 	void _canvas_layer_remove(CanvasLayer *p_canvas_layer);
 
 	void _drop_mouse_focus();
+	void _drop_physics_mouseover();
 
 	void _update_canvas_items(Node *p_node);