lib.sh: Make err_ always exit no matter what

Always certainly redundant, since if -u -e isn't
set, it'll continue to exit anyway.

However, we want to be pedantic about this, since
the safety of lbmk relies entirely on this function
NOT misbehaving.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/lib.sh

@@ -174,6 +174,6 @@ x_()
 
 err_()
 {
-	printf "ERROR %s: %s\n" "$0" "$1" 1>&2
+	[ $# -lt 1 ] || printf "ERROR %s: %s\n" "$0" "$1" 1>&2 || :
 	exit 1
 }