fixed check for USB serial monitor opened on the PC (using DTR)

sam/1.0.5/cores/arduino/USB/CDC.cpp

@@ -282,7 +282,7 @@ size_t Serial_::write(const uint8_t *buffer, size_t size)
 	// TODO - ZE - check behavior on different OSes and test what happens if an
 	// open connection isn't broken cleanly (cable is yanked out, host dies
 	// or locks up, or host virtual serial port hangs)
-	if (_usbLineInfo.lineState > 0)
+	if (_usbLineInfo.lineState & 0x01)
 	{
 		int r = USBD_Send(CDC_TX, buffer, size);
 
@@ -318,7 +318,7 @@ Serial_::operator bool()
 
 	bool result = false;
 
-	if (_usbLineInfo.lineState > 0)
+	if (_usbLineInfo.lineState & 0x01)
 	{
 		result = true;
 	}