attr: plug minor memory leak

Free the memory allocated for struct strbuf pathbuf when we're done.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

attr.c

@@ -555,6 +555,8 @@ static void prepare_attr_stack(const char *path, int dirlen)
 		}
 	}
 
+	strbuf_release(&pathbuf);
+
 	/*
 	 * Finally push the "info" one at the top of the stack.
 	 */