[21.4] Patch for consistent crash with Linux native sound on AMD64

[Aidan Kehoe]

 Ar an séú lá déag de mí na Nollaig, scríobh Stephen J. Turnbull: 

 > As long as the size_t data is solely used to communicate with external
 > code such as device drivers, it's best to use size_t explicitly (and
 > probably document it with a comment).  

The communication with the device drivers is by means of write(). Using
size_t with write() and propagation of unsignedness with that was exactly
our problem with size_t, if I remember it correctly. I admit it unlikely
that more than 2^^31 (or 2^^63) bytes of data will be written to a sound
card. 

-- 
Santa Maradona, priez pour moi!