Palettized image test.

src/util/reflist.c

@@ -30,7 +30,7 @@ ref_t refListLock(reflist_t *list) {
   assertFalse(refListIsFull(list), "Reference list is full");
 
   ref_t ref = list->refNext++;
-  assertTrue(ref > 0, "Reference ID overflow");
+  assertTrue(ref >= 0, "Reference ID overflow");
   assertTrue(ref < UINT16_MAX, "Reference ID too large.");
 
   bool_t empty = list->onNotEmpty && refListIsEmpty(list);