Bug Fix in modesReadFromClient()

The modesReadFromClient() funtion is called from modesReadFromClients(),
which in turn is called from backgroundTasks(). backgroundTasks() is
called from within the main processing loop.

However, modesReadFromClient() can and does block. It attempts to read
characters from the input stream, and loops whilst there was no error.
This stalls the main RTL processing loop until an error occurs. In order
to support simultaneous local reception (via our RTL dongle) and remote
forwarding (data received from the interweb) we cannot allow this
internet read to stall.

To fix this, in modesReadFromClient() attempt to read a buffer of data
(currently 0x400 bytes). If we get a full buffer of bytes, then process
them, and attempt to read another full buffer. Keep doing thios untill
we read only a partial buffer (less than 0x400 bytes). Process the
partial buffer bytes and return.

This allows us to occasionally process data that is arriving from the
internet (which is buffered anyway in the TCP stack), without blocking
local RTL dongle decoding.