`++cue` jet crashes the runtime when the sample is a cell

[dozreg-toplud]

Calling ++cue with a cell sample causes the runtime to crash non-recoverably:

(slum cue *^)

This is due to the fact that u3s_cue_atom is called without checking if its argument is an atom.

[joemfb]

Good catch.

[dozreg-toplud]

Another similar bug:

(slum max 0 0 0)
(slum min 0 0 0)

[dozreg-toplud]

Resolved with #836 merged to 409