setup.c: check that the pathspec magic ends with ")"

The previous code did not diagnose an incorrectly spelled ":(top"
as an error.

Signed-off-by: Andrew Wong <andrew.kw.w@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

setup.c

@@ -216,8 +216,9 @@ static const char *prefix_pathspec(const char *prefix, int prefixlen, const char
 				die("Invalid pathspec magic '%.*s' in '%s'",
 				    (int) len, copyfrom, elt);
 		}
-		if (*copyfrom == ')')
-			copyfrom++;
+		if (*copyfrom != ')')
+			die("Missing ')' at the end of pathspec magic in '%s'", elt);
+		copyfrom++;
 	} else {
 		/* shorthand */
 		for (copyfrom = elt + 1;