avcodec/mpegvideo_enc: Only enforce rc_max_available_vbv_use on first encoding attempt

This reduces repeatly re-encoding to achieve VBV compliance

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/hlsenc: fix outter typo

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