Fixes HWCDC::end() (#8247)

* Fixes HWCDC::end()

There is a missing `tx_lock = NULL;`

* Update HWCDC.cpp

Initialize rx_data_buf[] with zeros.

cores/esp32/HWCDC.cpp

@@ -28,7 +28,7 @@ ESP_EVENT_DEFINE_BASE(ARDUINO_HW_CDC_EVENTS);
 
 static RingbufHandle_t tx_ring_buf = NULL;
 static xQueueHandle rx_queue = NULL;
-static uint8_t rx_data_buf[64];
+static uint8_t rx_data_buf[64] = {0};
 static intr_handle_t intr_handle = NULL;
 static volatile bool initial_empty = false;
 static xSemaphoreHandle tx_lock = NULL;
@@ -195,6 +195,7 @@ void HWCDC::end()
     intr_handle = NULL;
     if(tx_lock != NULL) {
         vSemaphoreDelete(tx_lock);
+        tx_lock = NULL;
     }
     setRxBufferSize(0);
     setTxBufferSize(0);