Split _die in two methods

We need to do some stuff before AbstractDownloadItem._die runs.

qutebrowser/browser/downloads.py

@@ -327,6 +327,10 @@ class AbstractDownloadItem(QObject):
                         remaining=remaining, perc=perc, down=down,
                         total=total, errmsg=errmsg))
 
+    def _do_die(self):
+        """Do cleanup steps after a download has died."""
+        raise NotImplementedError
+
     def _die(self, msg):
         """Abort the download and emit an error."""
         assert not self.successful
@@ -350,6 +354,7 @@ class AbstractDownloadItem(QObject):
         if self._dead:
             return
         self._dead = True
+        self._do_die()
         self.error_msg = msg
         self.stats.finish()
         self.error.emit(msg)

qutebrowser/browser/qtnetworkdownloads.py

@@ -118,9 +118,8 @@ class DownloadItem(downloads.AbstractDownloadItem):
                               no_action=no_action, cancel_action=no_action,
                               abort_on=[self.cancelled, self.error])
 
-    def _die(self, msg):
+    def _do_die(self):
         """Abort the download and emit an error."""
-        super()._die(msg)
         self._read_timer.stop()
         self._reply.downloadProgress.disconnect()
         self._reply.finished.disconnect()