Cache SerialPort in SerialLoggerFactory (#83)

Author: oblaise

nanoFramework.Logging.Serial/SerialLoggerFactory.cs

@@ -49,12 +49,15 @@ public SerialLoggerFactory(
         /// <inheritdoc/>
         public ILogger CreateLogger(string categoryName)
         {
-            _serial = new SerialPort(_comPort);
-            _serial.BaudRate = _baudRate;
-            _serial.Parity = _parity;
-            _serial.StopBits = _stopBits;
-            _serial.Handshake = _handshake;
-            _serial.DataBits = _dataBits;
+            if (_serial is null)
+            {
+                _serial = new SerialPort(_comPort);
+                _serial.BaudRate = _baudRate;
+                _serial.Parity = _parity;
+                _serial.StopBits = _stopBits;
+                _serial.Handshake = _handshake;
+                _serial.DataBits = _dataBits;
+            }
             return new SerialLogger(ref _serial, categoryName);
         }