Sometimes receiving single zero byte

[dhalbert]

Why does #127 fix #126? As mentioned by @brentru in https://github.com/adafruit/Adafruit_CircuitPython_MiniMQTT/pull/127#issuecomment-1317271214 and following

@jinglemansweep Hi - thanks for fixing this issue. @dhalbert - I do not think this is a network or a MQTT spec issue, b"\x00 is rx'd after the call to res = self._sock_exact_recv(1).

Considering some in #126 are having issues with non-native wifi, it's possible (don't know, guessing right now) that the issue is within this library's local implementation of _sock_exact_recv() vs the native impl. of _sock_exact_recv() (cc @calcut ☝️ )

        # CPython socket module contains a timeout attribute
        if hasattr(self._socket_pool, "timeout"):
            try:
                res = self._sock_exact_recv(1)
            except self._socket_pool.timeout:
                return None
        else:  # socketpool, esp32spi
            try:
                res = self._sock_exact_recv(1)

For now, though, I think this is an OK temporary change and will cause clients to poll faster until we resolve why the socket is rcv'ing a bytearray on some clients.