eina_list: Avoid NULL pointer deref in eina_list_shuffle.

If we have a valid but empty, n = 0, list we never enter the loop
and shuffled_last might still be NULL. Avoid this case by checking
explicitly for n = 0 before.

src/lib/eina/eina_list.c

@@ -1111,6 +1111,9 @@ eina_list_shuffle(Eina_List *list, Eina_Random_Cb func)
    n = accounting->count;
    shuffled_list = shuffled_last = NULL;
 
+   if (n == 0)
+     return NULL;
+
    if (n == 1)
      return list;