replace: plug a memory leak

Recent update to for_each_replace_name() to make it use a strbuf in
place of a fixed buffer forgot to release the memory held by the
strbuf before leaving the function.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/replace.c b/builtin/replace.c
index 065515b..ab17668 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -120,6 +120,7 @@ static int for_each_replace_name(const char **argv, each_replace_name_fn fn)
 		if (fn(full_hex, ref.buf, &oid))
 			had_error = 1;
 	}
+	strbuf_release(&ref);
 	return had_error;
 }