FIX: make sure the QSocketNotifier is disabled

This fixes issues that Matplotlib was seeing with Qt5 + IPython with
PT on OSX (see https://github.com/matplotlib/matplotlib/issues/13066)

IPython/terminal/pt_inputhooks/qt.py

@@ -1,49 +1,53 b''
 import sys
 import os
 from IPython.external.qt_for_kernel import QtCore, QtGui
 
 # If we create a QApplication, keep a reference to it so that it doesn't get
 # garbage collected.
 _appref = None
 _already_warned = False
 
+
 def inputhook(context):
     global _appref
     app = QtCore.QCoreApplication.instance()
     if not app:
         if sys.platform == 'linux':
             if not os.environ.get('DISPLAY') \
                     and not os.environ.get('WAYLAND_DISPLAY'):
                 import warnings
                 global _already_warned
                 if not _already_warned:
                     _already_warned = True
                     warnings.warn(
                         'The DISPLAY or WAYLAND_DISPLAY environment variable is '
                         'not set or empty and Qt5 requires this environment '
                         'variable. Deactivate Qt5 code.'
                     )
                 return
         _appref = app = QtGui.QApplication([" "])
     event_loop = QtCore.QEventLoop(app)
 
     if sys.platform == 'win32':
         # The QSocketNotifier method doesn't appear to work on Windows.
         # Use polling instead.
         timer = QtCore.QTimer()
         timer.timeout.connect(event_loop.quit)
         while not context.input_is_ready():
             timer.start(50)  # 50 ms
             event_loop.exec_()
             timer.stop()
     else:
         # On POSIX platforms, we can use a file descriptor to quit the event
         # loop when there is input ready to read.
         notifier = QtCore.QSocketNotifier(context.fileno(),
                                           QtCore.QSocketNotifier.Read)
-        # connect the callback we care about before we turn it on
-        notifier.activated.connect(event_loop.exit)
-        notifier.setEnabled(True)
-        # only start the event loop we are not already flipped
-        if not context.input_is_ready():
-            event_loop.exec_()
+        try:
+            # connect the callback we care about before we turn it on
+            notifier.activated.connect(event_loop.exit)
+            notifier.setEnabled(True)
+            # only start the event loop we are not already flipped
+            if not context.input_is_ready():
+                event_loop.exec_()
+        finally:
+            notifier.setEnabled(False)