Use an early-abort in the USB_DeviceTask() function rather than wrapping the entire implementation in a conditional.

LUFA/Drivers/USB/Core/USBTask.c

@@ -60,8 +60,9 @@ void USB_USBTask(void)
 #if defined(USB_CAN_BE_DEVICE)
 static void USB_DeviceTask(void)
 {
-	if (USB_DeviceState != DEVICE_STATE_Unattached)
-	{
+	if (USB_DeviceState == DEVICE_STATE_Unattached)
+	  return;
+
 	uint8_t PrevEndpoint = Endpoint_GetCurrentEndpoint();
 
 	Endpoint_SelectEndpoint(ENDPOINT_CONTROLEP);
@@ -71,7 +72,6 @@ static void USB_DeviceTask(void)
 
 	Endpoint_SelectEndpoint(PrevEndpoint);
 }
-}
 #endif
 
 #if defined(USB_CAN_BE_HOST)