Merge branch 'Optimize/null_pointer_judgment_of_eb' into 'master'

esp_netif:optimize the null pointer judgment of eb

Closes IDF-4576

See merge request espressif/esp-idf!16934

components/esp_wifi/src/wifi_netif.c

@@ -48,7 +48,9 @@ static esp_err_t wifi_ap_receive(void *buffer, uint16_t len, void *eb)
 
 static void wifi_free(void *h, void* buffer)
 {
-    esp_wifi_internal_free_rx_buffer(buffer);
+    if (buffer) {
+        esp_wifi_internal_free_rx_buffer(buffer);
+    }
 }
 
 static esp_err_t wifi_transmit(void *h, void *buffer, size_t len)