vcs: Use key lookup to explode if key is not available.

The key has to be in the dictionary, otherwise something changed in the code
and expoding here is better than hiding the error.

rhodecode/lib/middleware/simplevcs.py

@@ -124,7 +124,7 b' class SimpleVCS(object):'
             self.acl_repo_name = '{base_name}/{repo_name}'.format(**match_dict)
             self.vcs_repo_name = '{base_name}/.__shadow_{repo_name}_pr-{pr_id}'.format(
                 **match_dict)
-            self.pr_id = match_dict.get('pr_id')
+            self.pr_id = match_dict['pr_id']
         else:
             self.acl_repo_name = self.url_repo_name
             self.vcs_repo_name = self.url_repo_name