Revert "Leave slug empty until we are sure media processing was successful."

This reverts commit f67611fb48.

For some reason, generating a slug here throws an integrity error during
a query when there is a duplicate slug.

mediagoblin/submit/views.py

@@ -78,6 +78,9 @@ def submit_start(request):
                 entry.tags = convert_to_tag_list_of_dicts(
                     submit_form.tags.data)
 
+                # Generate a slug from the title
+                entry.generate_slug()
+
                 queue_file = prepare_queue_task(request.app, entry, filename)
 
                 with queue_file: