Gerrit: Unset authenticated on unknown error

Let the server retry authentication on next update.

Change-Id: I22d9fcde2b501fc7c9b9d86bb9b656c73d3ee840
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/git/gerrit/gerritserver.cpp

@@ -323,6 +323,7 @@ bool GerritServer::resolveRoot()
             }
             break;
         default: // unknown error - fail
+            authenticated = false;
             return false;
         }
     }