misc/editor: Fix tempfile deleted on error / editor crash

This patch attempts to fix an issue where an error occuring in
misc/guiprocess or the editor process crashing would delete the
temporary file thus making it impossible to recover changes not commited
to the form field from the editor.

qutebrowser/misc/editor.py

@@ -58,6 +58,7 @@ class ExternalEditor(QObject):
             return
         try:
             os.close(self._oshandle)
+            if self._proc.exit_status() != QProcess.CrashExit:
                 os.remove(self._filename)
         except OSError as e:
             # NOTE: Do not replace this with "raise CommandError" as it's

qutebrowser/misc/guiprocess.py

@@ -151,3 +151,6 @@ class GUIProcess(QObject):
         else:
             message.error(self._win_id, "Error while spawning {}: {}.".format(
                           self._what, self._proc.error()), immediately=True)
+
+    def exit_status(self):
+        return self._proc.exitStatus()

tests/unit/misc/test_editor.py

@@ -91,19 +91,28 @@ class TestFileHandling:
         filename = editor._filename
         assert os.path.exists(filename)
 
+        editor._proc._proc.exitStatus = mock.Mock(
+                return_value=QProcess.CrashExit)
         editor._proc.finished.emit(1, QProcess.NormalExit)
 
-        assert not os.path.exists(filename)
+        assert os.path.exists(filename)
+
+        os.remove(filename)
 
     def test_crash(self, editor):
         """Test file handling when closing with a crash."""
         editor.edit("")
         filename = editor._filename
         assert os.path.exists(filename)
+
+        editor._proc._proc.exitStatus = mock.Mock(
+                return_value=QProcess.CrashExit)
         editor._proc.error.emit(QProcess.Crashed)
 
         editor._proc.finished.emit(0, QProcess.CrashExit)
-        assert not os.path.exists(filename)
+        assert os.path.exists(filename)
+
+        os.remove(filename)
 
     @pytest.mark.posix
     def test_unreadable(self, message_mock, editor):