http-push: fix missing "#ifdef USE_CURL_MULTI" around "is_running_queue"

As it is breaking the build when USE_CURL_MULTI is not defined.
Signed-off-by: NChristian Couder <chriscool@tuxfamily.org>
Signed-off-by: NTay Ray Chuan <rctay89@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

http-push.c

@@ -2297,7 +2297,9 @@ int main(int argc, char **argv)
 		repo->url = rewritten_url;
 	}
 
+#ifdef USE_CURL_MULTI
 	is_running_queue = 0;
+#endif
 
 	/* Verify DAV compliance/lock support */
 	if (!locking_available()) {