fix the displaying of the error dialogs

Exceptions which get raised in threads don't bubble up into the main code on
their own. So we either communicate them to the main loop or we handle them
directly in the thread. I'm going for the later for the moment because the
other way seems to be quite complex.

borg_qt/borg_interface.py

@@ -5,7 +5,7 @@ import json
 
 from PyQt5.QtCore import QThread
 
-from helper import BorgException
+from helper import BorgException, show_error
 
 
 class BorgQtThread(QThread):
@@ -46,7 +46,8 @@ class BorgQtThread(QThread):
                 return
             else:
                 err = json.loads(error)
-                raise BorgException(err['message'])
+                show_error(BorgException(err['message']))
+                self.stop()
 
 
 class ListThread(BorgQtThread):