apkgrel: pass -- to git with name of file in do_add

the name of the file can be ambiguous, as it might also be the name of a
branch. passing -- makes git look at it as a file only, and not a
potential branch.

apkgrel.in

@@ -45,7 +45,7 @@ do_add () {
 	local f= old=
 	for f; do
 		[ -n "$only_clean_git" ] \
-			&& [ -n "$(git diff --name-only "${f%/*}")" ] \
+			&& [ -n "$(git diff --name-only -- "${f%/*}")" ] \
 			&& continue
 		old=$(show_plain "$f")
 		case $old in