bug#30559: 26.0.91; grep-use-null-filename-separator customization

[Juri Linkov <juri@linkov.net>]

>> This is a request to push the patch to the emacs-26 release branch.
>
> OK.

Sorry, I forgot to do the same for zrgrep.  I already noticed earlier
that grep-use-null-filename-separator let-binding is missing here,
but forgot to test this to affirm the necessity to fix zrgrep too.
So this fix is needed for the release branch.

Eli, is it OK to push this patch to emacs-26 as well?

diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index 755c9c7..9b6ebee 100644
--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -1184,6 +1184,7 @@ zrgrep
 	   ;; by `grep-compute-defaults'.
 	   (grep-find-template nil)
 	   (grep-find-command nil)
+	   (grep-use-null-filename-separator nil)
 	   (grep-host-defaults-alist nil)
 	   ;; Use for `grep-read-files'
 	   (grep-files-aliases '(("all" . "* .*")