Merge pull request matplotlib#3360 from tacaswell/qApp_fix

BUG : modified logic on starting qApp

Author: jenshnielsen

lib/matplotlib/backends/backend_qt5.py

@@ -125,13 +125,13 @@ def _create_qApp():
     """
     Only one qApp can exist at a time, so check before creating one.
     """
-    if QtWidgets.QApplication.startingUp():
+
+    if qApp is None:
         if DEBUG:
             print("Starting up QApplication")
         global qApp
         app = QtWidgets.QApplication.instance()
         if app is None:
-
             # check for DISPLAY env variable on X11 build of Qt
             if hasattr(QtGui, "QX11Info"):
                 display = os.environ.get('DISPLAY')