Changelog-Fixed: Due to the imprecision of `htlc_max`'s type (`fp16_t`),
`capacity_bias()` can return `NaN` in some cases. This leads to a
runtime error when compiled with UBSan. Add a check against it.
Any file in this directory which is executable and whose name only
consists of alphanumeric characters, space, '.', '-' or '_' will be
automatically loaded when lightningd starts (unless suppressed with
commandline options).