Make pre_read imply invalidate=0

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/init.c b/init.c
index 07068d7..7681102 100644
--- a/init.c
+++ b/init.c
@@ -357,6 +357,9 @@
 	if (td->o.verify != VERIFY_NONE)
 		td->o.refill_buffers = 1;
 
+	if (td->o.pre_read)
+		td->o.invalidate_cache = 0;
+
 	return 0;
 }