branches/zip: buf_page_get_gen(): Reinitialize guess when re-entering the loop.

buf/buf0buf.c

@@ -1781,6 +1781,7 @@ wait_until_unfixed:
 			mutex_exit(&buf_pool->mutex);
 			os_thread_sleep(WAIT_FOR_READ);
 
+			guess = block;
 			goto loop;
 		}