-reverted Daniels commit to change mBufferPos - it has reintroduced heap corruption
 - you need to change reduce bytesRead by the number of bytes processed already
   when setting tryAgain to true
 - the remaining buffer is copied back to position 0 (see for statement 
   above changed code), so mBufferPos should be 0
   - ideally we would entirely remove this buffer copy
 - in else clause mBufferPos shouldn't be 0 - there may be a partial frame left
   over in the buffer
 - this section of code needs an in-depth review


git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@10166 ddefafc4-47db-0310-ae44-fa13212b10f2