[NTG-context] \setupcombinations[distance=none]

Minor bug (both mkiv and mkii): \setupcombinations[distance=none] is broken, whereas \setupcombinations[distance=0pt] is OK. Minimal example: \starttext \setupcombinations[distance=none] \startcombination[2] {M}{a} {M}{b} \stopcombination \stoptext ! Missing number, treated as zero. <to be read again> n \@@codistance ->n one \next ...\hskip \combinationparameter \c!distance &\docombination l.4 {M}{a} ?