Fix String.isSubstring The check that the substring is actually shorter than the argument was accidentally removed during the conversion from the old string representation.
Fix String.isSubstring
The check that the substring is actually shorter than the argument was accidentally removed
during the conversion from the old string representation.

dcjm/polyml,dcjm/polyml,polyml/polyml,polyml/polyml,dcjm/polyml,polyml/polyml,dcjm/polyml,polyml/polyml