fix same sized delta logic

The code favoring shallower deltas when size is equal was triggered
only when previous delta was also cached.  There should be no relation
between cached deltas and same sized deltas.
Signed-off-by: NNicolas Pitre <nico@cam.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -1389,21 +1389,25 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	if (!delta_buf)
 		return 0;
 
-	if (trg_entry->delta_data) {
+	if (trg_entry->delta) {
 		/* Prefer only shallower same-sized deltas. */
 		if (delta_size == trg_entry->delta_size &&
 		    src->depth + 1 >= trg->depth) {
 			free(delta_buf);
 			return 0;
 		}
-		delta_cache_size -= trg_entry->delta_size;
-		free(trg_entry->delta_data);
-		trg_entry->delta_data = NULL;
 	}
+
 	trg_entry->delta = src_entry;
 	trg_entry->delta_size = delta_size;
 	trg->depth = src->depth + 1;
 
+	if (trg_entry->delta_data) {
+		delta_cache_size -= trg_entry->delta_size;
+		free(trg_entry->delta_data);
+		trg_entry->delta_data = NULL;
+	}
+
 	if (delta_cacheable(src_size, trg_size, delta_size)) {
 		trg_entry->delta_data = xrealloc(delta_buf, delta_size);
 		delta_cache_size += trg_entry->delta_size;