Possible off-by-one bug in uwb_twr_tag could crash firmware on timeout

[stefanthorstenson]

If e.g. config.anchorListSize is 6, and resetting curr_anchor will occur when curr_anchor is 7, meaning that config.anchors[6] has been called, which should be one index too high (since index is zero-based).

This code is run only on timeout it seems.