remote: check config validity before creating rewrite struct

When parsing url.foo.insteadOf, we call make_rewrite() and only then
check to make sure the config value is a string (and return an error if
it isn't). This isn't quite a leak, because the struct we allocate is
part of a global array, but it does leave a funny half-finished struct.

In practice, it doesn't make much difference because we exit soon after
due to the config error anyway. But let's flip the order here to avoid
leaving a trap for somebody in the future.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

remote.c

@@ -335,14 +335,14 @@ static int handle_config(const char *key, const char *value, void *cb)
 		if (!name)
 			return 0;
 		if (!strcmp(subkey, "insteadof")) {
-			rewrite = make_rewrite(&rewrites, name, namelen);
 			if (!value)
 				return config_error_nonbool(key);
+			rewrite = make_rewrite(&rewrites, name, namelen);
 			add_instead_of(rewrite, xstrdup(value));
 		} else if (!strcmp(subkey, "pushinsteadof")) {
-			rewrite = make_rewrite(&rewrites_push, name, namelen);
 			if (!value)
 				return config_error_nonbool(key);
+			rewrite = make_rewrite(&rewrites_push, name, namelen);
 			add_instead_of(rewrite, xstrdup(value));
 		}
 	}