avcodec: use block_Realloc() on input blocks.
avcodec: use block_Realloc() on input blocks.

This kills a memory copy in most cases (FFMPEG input padding is the same
as VLC block padding, at least on my system).

jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,shyamalschandra/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,jomanmuk/vlc-2.2,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,vlc-mirror/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc,jomanmuk/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,vlc-mirror/vlc-2.1,shyamalschandra/vlc,krichter722/vlc,jomanmuk/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,xkfz007/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,shyamalschandra/vlc