Fix crash when removing download in closed window

When a download is finished with `removed-finished-download` set to a
delay, it's removed via a singleshot QTimer.

However, when the window was closed in the meantime, the slot still was
executed by Qt, even though the DownloadManager was already deleted.

Fixes #1242

CHANGELOG.asciidoc

@@ -70,6 +70,8 @@ Fixed
 - Fixed crash when unbinding key from a section which doesn't exist in the config
 - Fixed report window after a segfault
 - Fixed some directory browser issues on Windows
+- Fixed crash when closing a window with a finished download and delayed
+  `remove-finished-downloads` setting.
 
 Removed
 ~~~~~~~

qutebrowser/browser/downloads.py

@@ -27,6 +27,7 @@ import shutil
 import functools
 import collections
 
+import sip
 from PyQt5.QtCore import (pyqtSlot, pyqtSignal, QObject, QTimer,
                           Qt, QVariant, QAbstractListModel, QModelIndex, QUrl)
 from PyQt5.QtGui import QDesktopServices
@@ -1130,6 +1131,9 @@ class DownloadManager(QAbstractListModel):
 
     def remove_item(self, download):
         """Remove a given download."""
+        if sip.isdeleted(self):
+            # https://github.com/The-Compiler/qutebrowser/issues/1242
+            return
         try:
             idx = self.downloads.index(download)
         except ValueError:

tests/integration/features/downloads.feature

@@ -161,3 +161,13 @@ Feature: Downloading things from a website.
         When I run :download http://localhost:(port)/drip?numbytes=128&duration=5
         And I run :download-open with count 1
         Then the error "Download 1 is not done!" should be shown
+        
+    ## https://github.com/The-Compiler/qutebrowser/issues/1242
+
+    Scenario: Closing window with remove-finished-downloads timeout
+        When I set ui -> remove-finished-downloads to 500
+        And I open data/downloads/download.bin in a new window
+        And I wait until the download is finished
+        And I run :close
+        And I wait 0.5s
+        Then no crash should happen