remote-curl: do not call fetch-pack when using gvfs-helper

When using the GVFS protocol, we should _never_ call "git fetch-pack"
to attempt downloading a pack-file via the regular Git protocol. It
appears that the mechanism that prevented this in the VFS for Git
world is due to the read-object hook populating the commits at the
new ref tips in a different way than the gvfs-helper does.

By acting as if the fetch-pack succeeds here in remote-curl, we
prevent a failed fetch.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

remote-curl.c

@@ -1169,6 +1169,9 @@ static int fetch_git(struct discovery *heads,
 	struct strvec args = STRVEC_INIT;
 	struct strbuf rpc_result = STRBUF_INIT;
 
+	if (core_use_gvfs_helper)
+		return 0;
+
 	strvec_pushl(&args, "fetch-pack", "--stateless-rpc",
 		     "--stdin", "--lock-pack", NULL);
 	if (options.followtags)