bug#18266: Bug#758105: bug#18266: Bug#758105: bug#18266: grep -P and invalid exits with error

[Paul Eggert]

Santiago wrote:

Another solution would be to don't check if binary files are valid
(passing PCRE_NO_UTF8_CHECK to pcre_exec), but I don't know if that'd
avoid security holes

It wouldn't.  (We already tried it.)