str2str does not always detect disconnection when waiting for NTRIP response from caster

[Jef239]

Error in recv_nb procedure. This procedure does select and recv and returns one of three options:

ret>0 - n bytes received
ret<0 - error
ret==0 - nothing received

The arrival of FIN (disconnect) is encoded as a return of -1 with errno==0. However, if errno!=0 before the call, it is not cleared when executing recv_nb. And then the situation is treated as an error, not as a disconnect. If errno was EGAIN, then the disconnect is not detected at all.

recv_nb.patch