Indexing sometimes breaks for unrecognised files in the irwins directory

[ya64]

Indexing sometimes breaks in v1.1.0 when there is a file that is not in the traditional irwin format (eg., #200 Johny Bravo HD Irwin.png)

The following exception is thrown:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -2
        at java.lang.String.substring(Unknown Source)
        at com.github.ya64.IrwinBot.Irwin.getNumberFromName(Irwin.java:55)
        at com.github.ya64.IrwinBot.IrwinLibrary.init(IrwinLibrary.java:28)
        at com.github.ya64.IrwinBot.Main.main(Main.java:52)