The ``reset`` and ``read`` pins should be optional, but the espressif
code had several places where it assumed they are not, and a bug that
caused a crash on ``release_displays`` if they were made optional.
The bug was caused by the fields for storing pin numbers being set
to ``NO_PIN``, which has value of -1, while the fields have type
``uint8_t``. That set the actual value to 255, and a subsequent
comparison to ``NO_PIN`` returned false.
