x-list.c: null-returning function malloc() was called without checking

Signed-off-by: Oliver McFadden <oliver.mcfadden@nokia.com>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>

hw/xquartz/xpr/x-list.c

@@ -97,6 +97,7 @@ X_PFX (list_prepend) (x_list *lst, void *data)
         int i;
 
         b = malloc (sizeof (x_list_block));
+        assert(b != NULL);
 
         for (i = 0; i < NODES_PER_BLOCK - 1; i++)
             b->l[i].next = &(b->l[i+1]);