Fixed error in calculation of maximal skeleton path length.

Fixed error in calculation of maximal skeleton path length.

The error was found by slyfox's fuzzer (a randomly-generated skeleton test).

The bug in the code was, apparently, too early modification of the state's
estimated maximal distance to the end states: the distance was set before
all of the state's children were processed, which resulted in aborting the
accumulation of distance from the remaining children, and, as a consequence,
shorter than necessary max distance for the root itself.