Perform req_padding() before searching for a fixed list.

custom_malloc.c

@@ -20,7 +20,7 @@ void * custom_malloc(heap_t* heap, size_t size) {
     posix_lock(heap);
 #endif /* HAVE_LOCKS */
 
-    fixed_list_id = map_size_to_list(heap, size);
+    fixed_list_id = map_size_to_list(heap, req_padding(size));
 
     // If a fixed list is found, do a first fit
     if(fixed_list_id != -1) {