sexpr: return negated errnos on list to array conversion failures
sexpr: return negated errnos on list to array conversion failures

This way, we can differentiate if the failure was because of not enough
memory or if the input value was not a list.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc