push: Correctly initialize nonfastforward in transport_push.

The variable is assigned unconditionally in print_push_status, but
print_push_status is not reached by all codepaths. In particular, this
fixes a bug where "git push ... nonexisting-branch" was complaining about
non-fast forward.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport.c

@@ -1001,8 +1001,9 @@ int transport_set_option(struct transport *transport,
 
 int transport_push(struct transport *transport,
 		   int refspec_nr, const char **refspec, int flags,
-		   int * nonfastforward)
+		   int *nonfastforward)
 {
+	*nonfastforward = 0;
 	verify_remote_names(refspec_nr, refspec);
 
 	if (transport->push)