'safe' does not capture binding error

[masak]

> (safe (id D D))
Error: ('unboundb D)
> (bel '(safe (id D D)))
nil

The first one should of course not throw an error but return nil, just like the second one.

(Going to file this issue even though, at the time of writing, that last evaluation hasn't come back with a result, 90 minutes later. Guessing eif takes a lot of time to run on two layers of Bel interpreter.)