widget: Fix an error on mouse press when widget has no basic layout

... and therefore no message_bar

Author: ales-erjavec

Orange/widgets/tests/test_widget.py

@@ -5,10 +5,10 @@
 
 from unittest.mock import patch, MagicMock
 
-from AnyQt.QtCore import QRect, QByteArray, QObject, pyqtSignal
+from AnyQt.QtCore import Qt, QPoint, QRect, QByteArray, QObject, pyqtSignal
 from AnyQt.QtGui import QShowEvent
 from AnyQt.QtWidgets import QAction
-from AnyQt.QtTest import QSignalSpy
+from AnyQt.QtTest import QSignalSpy, QTest
 
 from Orange.widgets.gui import OWComponent
 from Orange.widgets.settings import Setting, SettingProvider
@@ -92,6 +92,7 @@ class TestWidget2(OWWidget):
 
         w = TestWidget2()
         w.showEvent(QShowEvent())
+        QTest.mousePress(w, Qt.LeftButton, Qt.NoModifier, QPoint(1, 1))
 
     def test_store_restore_layout_geom(self):
         class Widget(OWWidget):

Orange/widgets/widget.py

@@ -827,7 +827,8 @@ def closeEvent(self, event):
 
     def mousePressEvent(self, event):
         """ Flash message bar icon on mouse press """
-        self.message_bar.flashIcon()
+        if self.message_bar is not None:
+            self.message_bar.flashIcon()
         event.ignore()
 
     def setVisible(self, visible):