detect buffer "overflow" when delivering immediate events and queue remainder for...

detect buffer "overflow" when delivering immediate events and queue remainder for delivery next time (though without actually requeing - just leave ringbuffer ptrs/indexes where they are. required some deep but minor changes in how MidiRingBuffer::read() works, so that we can detect if we're going to be able to deliver an event before we actually read any of its data. Peek FTW!

git-svn-id: svn://localhost/ardour2/branches/3.0@9629 d708f5d6-7413-0410-9779-e7cbd77b26cf