subtractSky1d mishandles a length mismatch between pfsArm and pfsConfig

After

from pfs.drp.stella.subtractSky1d import subtractSky1d

fiberId = 1443
dataId=dict(visit=110478, spectrograph=3, arm='r')

pfsConfig = butler.get("pfsConfig", dataId)

pfsArm = butler.get("pfsArm", dataId)
sky1d = butler.get("sky1d", dataId)

pfsConfig = pfsConfig.select(fiberId=fiberId)

a subtractSky1d(pfsArm, pfsConfig, sky1d) call does the wrong thing. Looking at the code, the first line is

sky = sky1d(spectra.wavelength, pfsConfig.select(fiberId=spectra.fiberId))

which returns a (600, 4176) array with only the first row set so the fiberId in the pfsConfig is not (in general) sky-subtracted.

The correct behaviour isn't obvious, an exception on the mismatch would be reasonable, or only sky subtract the fibres in the pfsConfig.