JWeb1TSearcher hides errors when data could not be found?

JWeb1TSearcher returns 0 if an index map file could not be found and -1 if an index file could not be found. That seems odd. I think it would be better to throw an IOException in that case. If that is not desirable, it should probably return 0 in both cases or throw specific exceptions.

(originally reported by Richard Eckart, but I don't want to use the issue exporter for a single issue :)
