Speeds up seeking mp3's on large files.

Thanks to Andrew Talbot for spotting this.

Some cards/drivers like ATI and the Geforce 8 driver return an error in
this case, make the test accept that. This lifts some constraints we
have to care for in WineD3D and removes one of the requirement for the
packing shader. We still need the packing shader for vs_1_1 -> ps_3_0
mapping and for indirect pixel shader varying addressing though.