Update WiFiClient.cpp

[Vigeant]

fixed the connected() function so that it only checks errno if recv returns a value of -1.

"in the even of an error, errno is set to indicate the error" --manpage

This fixes the ESP32 Webserver when dealing with a modern webserver with a slow SD card.

[me-no-dev]

thanks :)

[NathanSweet]

Why is _connected = true; here? IMO an unexpected error should disconnect.

              default:
                  log_i("Unexpected: RES: %d, ERR: %d", res, errno);
                  _connected = true;
                  break;

I call client.connected() every loop. When my client disconnects, I'm getting flooded with:

14:29:00.846 -> [615859][I][WiFiClient.cpp:531] connected(): Unexpected: RES: -1, ERR: 9
14:44:00.216 -> [ 58760][E][WiFiClient.cpp:477] available(): fail on fd 0, errno: 9, "Bad file number"

Error 9 seems to be "bad file number" and so the client should be considered disconnected.