Fix #976: IBC virtual buffer reset for large CUs
A fix for https://jvet.hhi.fraunhofer.de/trac/vvc/ticket/976 to handle the case when CU size is larger than VPDU size.
Edited by Frank Bossen
A fix for https://jvet.hhi.fraunhofer.de/trac/vvc/ticket/976 to handle the case when CU size is larger than VPDU size.