Do not log the exception before attempting an non-blocking dial

[olivierpelet]

When the block argument is not specified or is set to None during a call to dial(), the library tries to do a blocking connection first.
If a pynng.ConnectionRefused occurs, the exception is logged using the global logger and then a non-blocking connection is attempted.

In my opinion the exception should not be logged (especially using the global logger).
I've spent 2 hours figuring out that the exception displayed in my terminal does not occur in my code and is "normal" because I did not specified the block argument 😀

Here a small code example:

from pynng import Req0, NNGException

try:
    with Req0(dial="tcp://127.0.0.1:9093") as sock:
        sock.send_timeout = 3000
        sock.recv_timeout = 3000
        sock.send(b"my_data")
except NNGException as err:
    print(f"Exception occured in my code: {err}")

The output without this patch:

Synchronous dial failed; attempting asynchronous now
Traceback (most recent call last):
  File "/home/olivier/dev/tests/pynng-fix/pynng-master/pynng/nng.py", line 374, in dial
    return self.dial(address, block=True)
  File "/home/olivier/dev/tests/pynng-fix/pynng-master/pynng/nng.py", line 371, in dial
    return self._dial(address, flags=0)
  File "/home/olivier/dev/tests/pynng-fix/pynng-master/pynng/nng.py", line 390, in _dial
    check_err(ret)
  File "/home/olivier/dev/tests/pynng-fix/pynng-master/pynng/exceptions.py", line 201, in check_err
    raise exc(string, err)
pynng.exceptions.ConnectionRefused: Connection refused
Exception occured in my code: Timed out

The output with this patch:

Exception occured in my code: Timed out