views: Return Http404 if patch not found

Otherwise exception DoesNotExist shows error 500 on Apache

Signed-off-by: Andriy Gelman <andriy.gelman@gmail.com>
Signed-off-by: Stephen Finucane <stephen@that.guru>
Closes: #343

Author: talih0

patchwork/views/patch.py

@@ -41,15 +41,15 @@ def patch_detail(request, project_id, msgid):
     # redirect to cover letters where necessary
     try:
         patch = Patch.objects.get(project_id=project.id, msgid=db_msgid)
-    except Patch.DoesNotExist as exc:
+    except Patch.DoesNotExist:
         submissions = Submission.objects.filter(project_id=project.id,
                                                 msgid=db_msgid)
         if submissions:
             return HttpResponseRedirect(
                 reverse('cover-detail',
                         kwargs={'project_id': project.linkname,
                                 'msgid': msgid}))
-        raise exc
+        raise Http404('Patch does not exist')
 
     editable = patch.is_editable(request.user)
     context = {

releasenotes/notes/issue-343-cb591d031cd58b61.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Previously, attempting to retrieve a patch that did not exist would result
+    in a ``HTTP 500`` (Internal Server Error) being raised. This has been
+    corrected and a ``HTTP 404`` (Not Found) is now raised instead.