[NFCI][ValueTracking] getUnderlyingObject(): gracefully handle cycles

Normally, this function just doesn't bother about cycles,
and hopes that the caller supplied small-enough depth
so that at worst it will take a potentially large,
but limited amount of time. But that obviously doesn't work
if there is no depth limit.

This reapples 36f1c3db,
but without asserting, just bailout once cycle is detected.