There's another regcomp code block coming in this function that needs
the same error handling. This function can help avoid duplicating
error handling code.
Helped-by: Jeff King <peff@peff.com> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>