The current Decimal type does not support infinities. That said, the init you're attempting to use should not enter an infinite loop, either (CC @itaiferber, @Philippe_Hausler).
FWIW, this currently matches the behavior on Darwin, but I do think that trapping is likely better than looping infinitely. This is tracked by SR-3126 — we'd likely need to update the implementation on Darwin in tandem for consistency.