Bug fix: inter-tx split cause desync with bottomup partition search
Bug fix: inter-tx split cause desync with bottomup partition search

- This fix is requied in order to merge open-partition, as well as
future enablement of inter-tx for lower speeds which uses bottomup
partition search.

- The cause of desync was related to the enforcement of skip when a
partition is not skip but no coefficients are coded. In such case,
inter-tx split is not possible (becauses no coefficients exist) thus
tx_size and tx_type should be set accordingly.

xiph/rav1e,xiph/rav1e