Fix unintended buffer canceling

If 'batched dequeue' fails Surface reverts by calling batched cancel
buffer. However, 'slot' has meaningless information as 'batched dequeue'
failed in the previous step. It leads to the unintended buffer canceling
on the slot 0, if the transaction involves H2B/B2H converter.

Bug: 259493167
Test: atest libgui_test
Change-Id: Ia29605fe1e26ef00b94cc6c08a2310b9c095567f