lavf/apngdec: print currently unsupported in-stream tags in a more readable form

Also use length and not stream position

Reviewed-by: Benoit Fouet <benoit.fouet@free.fr>
Signed-off-by: James Almer <jamrial@gmail.com>
lavc/mss1: fix mem leak in case of init failure

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
lavc/rv30: fix mem leak in case of init failure

Also replaced return -1 with return AVERROR(EINVAL)

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>