Previously buffers were dropped, and data was not copied to
newly allocated buffers. As side-effect the read-offset was not
adjusted either.
The distance between read and write-pointer needs to be maintained
(delay does not change). This needs to be accounted for, when the
buffer increases while read->write wraps around the old (smaller)
buffer. Previously this triggered an assert (in line 180)
cd5f70e69a