fix: output very last picture in sequence
fix bug that wrong slice headers may be accessed from picture
fix intra-prediction with multiple slices
intra-prediction speed improvement for border pixel extraction
fix parallel-merge-level position checks
fix bug with active singleMCLFlag (new definition in standard)
move RefPicList to image data since it is the same for all slices
fix cleanup of slice headers in multi-slice pictures
show error code
simplify similar BI-prediction MVs to single prediction only when weighted prediction if off