aioble/examples/temp_client.py: Check connection before reading temp.

Only read from the temp characteristic if the connection is still active.
Improves the example by avoiding a TypeError exception if/when the sensor
disconnects.

micropython/bluetooth/aioble/examples/temp_client.py

@@ -55,7 +55,7 @@ async def main():
             print("Timeout discovering services/characteristics")
             return
 
-        while True:
+        while connection.is_connected():
             temp_deg_c = _decode_temperature(await temp_characteristic.read())
             print("Temperature: {:.2f}".format(temp_deg_c))
             await asyncio.sleep_ms(1000)