[IBC] Early return from candidate list accordingly to mvp_l0_flag
In IBC when general_merge_flag is 0, the block vector candidate will be chosen accordingly to mvp_l0_flag. Thus we can avoid adding a second candidate when mvp_l0_flag is 0.
In IBC when general_merge_flag is 0, the block vector candidate will be chosen accordingly to mvp_l0_flag. Thus we can avoid adding a second candidate when mvp_l0_flag is 0.