Fix issue where STM32F4 USB could lock up if TX during heavy RX

Author: gfwilliams

ChangeLog

@@ -72,6 +72,7 @@
             nRF5x: Allow NRF.setScan and NRF.findDevices to take the same search filters NRF.requestDevice does (fix #1496)
             Fix buffer overrun if we have to reallocate a pointer to argument lists when calling a function (fix #1491)
             Fix stack overflow if executing regex full of hundreds of open brackets (fix #1487)
+            Fix issue where STM32F4 USB could lock up if TX during heavy RX
 
      1v99 : Increase jslMatch error buffer size to handle "UNFINISHED TEMPLATE LITERAL" string (#1426)
             nRF5x: Make FlashWrite cope with flash writes > 4k

targetlibs/stm32usb/usbd_cdc_hid.c

@@ -659,7 +659,7 @@ static uint8_t  USBD_CDC_HID_SOF (struct _USBD_HandleTypeDef *pdev) {
                            CDC_DATA_FS_OUT_PACKET_SIZE);
   }
 
-  if (!handle->cdcState & CDC_WRITE_TX_WAIT) {
+  if (!(handle->cdcState & CDC_WRITE_TX_WAIT)) {
     // try and fill the buffer
     unsigned int len = 0;
     int c;