Fix bad interaction with file open/close and queuing

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 5ee43e0..47b6d48 100644
--- a/fio.h
+++ b/fio.h
@@ -980,6 +980,12 @@
 	}	\
 } while (0)
 
+static inline void fio_file_reset(struct fio_file *f)
+{
+	f->last_free_lookup = 0;
+	f->last_pos = f->file_offset;
+}
+
 static inline void clear_error(struct thread_data *td)
 {
 	td->error = 0;