n'th Fibonacci builtin Åf doesn't work on decimals

[kcruijss]

See title (although 0.0 and 1.0 do seem to work for some reason..)

(Found in this second 05AB1E answer of mine.)

Try it online.
Attempt it online. (This uses a newer 05AB1E version where some of the bugs have been fixed that are still present on TIO, but it also happens here.)