Minor tweak

This makes it so that '.nlogo' file URLs are tried last by the compilation API, which prevents their error messages from being overwritten by the means attempted
Fixing bug in '.nlogo' URL reading

I think it was defaulting to UTF-8 as the codec before.  But... we don't
want that.  ISO8859 is the wider codec, and, without it, I was getting
URL-readings throwing `MalformedCharsetException`s.  Simple fix.