Use only 1 UART pin (RX only or TX only)

On and ESP32 my goal is to use a UART with only a RX pin or TX pin. Right now configuring a UART on ESP32 will fail unless both pins are specified whereas the IDF allows passing UART_PIN_NO_CHANGE (-1) for unused pins.

I believe this comes from mongoose-os/esp32_uart.c at 1b88d6d7205e24f220976451b2cd52ad9c22faaa · cesanta/mongoose-os · GitHub this line. Should this allow either but not both to be < 0?