Stack overflow when writing ogg with long frames

[littlecattle]

Should be allocated on heap to avoid stack overflow caused by long frames?

vorbis/lib/block.c

Line 420 in 84c0236

float *work=alloca(v->pcm_current*sizeof(*work));

[ssaue]

This bug is particularly critical on Windows which appears to have a smaller stack by default

[AlexTMjugador]

I have fixed this on #104.