Do not crash with a NULL pointer dereference when dcngettext()
is called with NULL msgid[12] arguments.

Fix for https://github.com/void-linux/void-packages/issues/12042
and probably others.

	--xtraeme

--- a/src/locale/__mo_lookup.c.orig	2019-06-26 09:55:36.843012674 +0200
+++ b/src/locale/__mo_lookup.c	2019-06-26 09:56:11.529443955 +0200
@@ -13,7 +13,7 @@ const char *__mo_lookup(const void *p, s
 	uint32_t b = 0, n = swapc(mo[2], sw);
 	uint32_t o = swapc(mo[3], sw);
 	uint32_t t = swapc(mo[4], sw);
-	if (n>=size/4 || o>=size-4*n || t>=size-4*n || ((o|t)%4))
+	if (!s || n>=size/4 || o>=size-4*n || t>=size-4*n || ((o|t)%4))
 		return 0;
 	o/=4;
 	t/=4;
