fix(esp-tls): Reduce parameter check for esp_tls_conn_read

Previously the *data parameters of esp_tls_conn_read
    was required to be non-NULL after espressif/esp-idf!28358.
    This prevents users from using a functionality in esp_tls_conn_read
    where calling `esp_tls_conn_read(ctx, NULL, 0);` triggers the
    transfer of contents from tcp layer to mbedtls (ssl) layer.
    After this the user can read the contents from
    esp_tls_get_bytes_avail().
    This commit removes the additional NULL check on the data field
    to keep this functionality enabled.

components/esp-tls/esp_tls.c

@@ -132,7 +132,7 @@ static ssize_t tcp_write(esp_tls_t *tls, const char *data, size_t datalen)
 
 ssize_t esp_tls_conn_read(esp_tls_t *tls, void  *data, size_t datalen)
 {
-    if (!tls || !data) {
+    if (!tls) {
         return -1;
     }
     return tls->read(tls, (char *)data, datalen);