builtin/send-pack: populate the default configs

builtin/send-pack didn't call git_default_config, and because of this
git push --signed didn't respect the username and email in gitconfig in
the HTTP transport.

Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/send-pack.c

@@ -120,7 +120,7 @@ static int send_pack_config(const char *k, const char *v, void *cb)
 			}
 		}
 	}
-	return 0;
+	return git_default_config(k, v, cb);
 }
 
 int cmd_send_pack(int argc, const char **argv, const char *prefix)