read-cache: fix memory leak in do_write_index

The previous_name_buf was never getting released when there
was an error in ce_write_entry or allow was false and execution
was returned to the caller.

Signed-off-by: Kevin Willford <kewillf@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

read-cache.c

@@ -2192,7 +2192,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	int newfd = tempfile->fd;
 	git_SHA_CTX c;
 	struct cache_header hdr;
-	int i, err, removed, extended, hdr_version;
+	int i, err = 0, removed, extended, hdr_version;
 	struct cache_entry **cache = istate->cache;
 	int entries = istate->cache_nr;
 	struct stat st;
@@ -2247,15 +2247,21 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 			if (allow)
 				warning(msg, ce->name);
 			else
-				return error(msg, ce->name);
+				err = error(msg, ce->name);
 
 			drop_cache_tree = 1;
 		}
 		if (ce_write_entry(&c, newfd, ce, previous_name) < 0)
-			return -1;
+			err = -1;
+
+		if (err)
+			break;
 	}
 	strbuf_release(&previous_name_buf);
 
+	if (err)
+		return err;
+
 	/* Write extension data here */
 	if (!strip_extensions && istate->split_index) {
 		struct strbuf sb = STRBUF_INIT;