[FL-1104] Fix NFC crash and missing NfcMessageTypeDeviceNotFound event (#400)

* Remove asserts from platformProtectST25RComm, fix issue with concurrent access.
* NFC Worker: fix bug in nfc_worker_poll causing worker to skip sending ofNfcMessageTypeDeviceNotFound event
* Fix python linter: stick to old beta

.github/workflows/black.yml

@@ -12,4 +12,4 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
-      - uses: psf/black@stable
+      - uses: psf/black@20.8b1

applications/nfc/nfc_worker.c

@@ -84,7 +84,7 @@ void nfc_worker_poll(NfcWorker* nfc_worker, uint8_t cycles) {
         is_found |= nfc_worker_nfcf_poll(nfc_worker);
         is_found |= nfc_worker_nfcv_poll(nfc_worker);
         rfalFieldOff();
-        cycles--;
+        if(cycles > 0) cycles--;
         if((!is_found) && (!cycles)) {
             NfcMessage message;
             message.type = NfcMessageTypeDeviceNotFound;

lib/ST25RFAL002/platform.c

@@ -37,6 +37,7 @@ void platformSetIrqCallback(PlatformIrqCallback callback) {
 }
 
 HAL_StatusTypeDef platformSpiTxRx(const uint8_t *txBuf, uint8_t *rxBuf, uint16_t len) {
+    furi_assert(platform_st25r3916);
     bool ret = false;
     if (txBuf && rxBuf) {
         ret = api_hal_spi_bus_trx(platform_st25r3916->bus, (uint8_t*)txBuf, rxBuf, len, 1000);
@@ -55,12 +56,10 @@ HAL_StatusTypeDef platformSpiTxRx(const uint8_t *txBuf, uint8_t *rxBuf, uint16_t
 }
 
 void platformProtectST25RComm() {
-    furi_assert(platform_st25r3916 == NULL);
     platform_st25r3916 = (ApiHalSpiDevice*)api_hal_spi_device_get(ApiHalSpiDeviceIdNfc);
 }
 
 void platformUnprotectST25RComm() {
     furi_assert(platform_st25r3916);
     api_hal_spi_device_return(platform_st25r3916);
-    platform_st25r3916 = NULL;
 }