iolog: skip max_bs[rw] increment for rw == DDIR_INVAL

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/iolog.c b/iolog.c
index e805eae..1eb89b2 100644
--- a/iolog.c
+++ b/iolog.c
@@ -371,7 +371,7 @@
 		} else {
 			ipo->offset = offset;
 			ipo->len = bytes;
-			if (bytes > td->o.max_bs[rw])
+			if (rw != DDIR_INVAL && bytes > td->o.max_bs[rw])
 				td->o.max_bs[rw] = bytes;
 			ipo->fileno = fileno;
 			ipo->file_action = file_action;