String index out of range: -1 in TfIdfCalculator when processing WikiLSHTC-325K datasets

[mwydmuch]

When following the instruction from readme.txt for WikiLSHTC-325K datasets from the XMLC repo I've encountered the following error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
	at java.lang.String.substring(String.java:1955)
	at TfIdfCalculator.convertLibSvmToTfIdf(TfIdfCalculator.java:57)
	at TfIdfCalculator.main(TfIdfCalculator.java:211)

The same steps work for other datasets I've tested so far: Eurlex, AmazonCat, Wiki10, WikipediaLarge, and Amazon.