vd_lavc: fix decoder init failure path

libavcodec decoder initialization failure caused a segfault, because it
wasn't properly reported back in init().

Also remove the return value from init_avctx(), which actually makes
things simpler. Instead, ctx->avctx can be checked to see whether
initialization was ok.
demux_mkv: fix segfault issue playing back VC1 in a mkv

This bug was introduced in commit 06eee1b.
mplayer: put space before encoding part of status line

Also, the trailing space isn't needed.