fix confirm-quit=downloads with finished downloads

Issue #846

.rowCount() returns all downloads, even the finished ones that have not
yet been removed from the list. For confirming the quit event, we should
only consider downloads that are still running.

qutebrowser/browser/downloads.py

@@ -1238,3 +1238,11 @@ class DownloadManager(QAbstractListModel):
             # We don't have children
             return 0
         return len(self.downloads)
+
+    def running_downloads(self):
+        """Return the amount of still running downloads.
+
+        Return:
+            The number of unfinished downloads.
+        """
+        return len([1 for download in self.downloads if not download.done])

qutebrowser/mainwindow/mainwindow.py

@@ -413,7 +413,7 @@ class MainWindow(QWidget):
         tab_count = self.tabbed_browser.count()
         download_manager = objreg.get('download-manager', scope='window',
                                       window=self.win_id)
-        download_count = download_manager.rowCount()
+        download_count = download_manager.running_downloads()
         quit_texts = []
         # Ask if multiple-tabs are open
         if 'multiple-tabs' in confirm_quit and tab_count > 1: