avcodec/hevc: Export picture type

This only uses the first slice, improvement here is welcome
analyzing all slices the trivial way would interfere with threads

Fixes Ticket3185

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/h261: move b_stride/b_xy under the if() where they are used

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>