Increased the size of the FIFO that acts as the intermediate between writers and the MidiBuffer. Changed
implementation of ::write() to notice if MidiBuffer::push_back() fails, and then just leave data queued
for subsequent calls to ::flush_output_fifo().
Note: the logic here will be broken by invalid events/data, which ALSO cause MidiBuffer::push_back() to
return false. That needs fixing
f74eab854a