internal error: ArrayIndexOutOfBoundsException with imported Lexers

Getting this ArrayIndexOutOfBoundsException while trying to generate a Parser and it's Lexers

The tool seems to have issues with the HT fragment inside the WS fragment of the ZConfHelpLexer.g grammar

```
8:57:35 PM: Executing external task 'generateGrammarSource'...
error(10): internal error: jconfig/src/main/antlr3/com/initvoid/jconfig/zconf/ZConfParser.g : java.lang.ArrayIndexOutOfBoundsException: 2
org.antlr.tool.Rule.trackRuleReferenceInAlt(Rule.java:294)
org.antlr.tool.Grammar.altReferencesRule(Grammar.java:2011)
org.antlr.grammar.v3.DefineGrammarItemsWalker.atom(DefineGrammarItemsWalker.java:3197)
org.antlr.grammar.v3.DefineGrammarItemsWalker.element(DefineGrammarItemsWalker.java:2089)
org.antlr.grammar.v3.DefineGrammarItemsWalker.alternative(DefineGrammarItemsWalker.java:1738)
org.antlr.grammar.v3.DefineGrammarItemsWalker.block(DefineGrammarItemsWalker.java:1639)
org.antlr.grammar.v3.DefineGrammarItemsWalker.rule(DefineGrammarItemsWalker.java:1254)
org.antlr.grammar.v3.DefineGrammarItemsWalker.rules(DefineGrammarItemsWalker.java:981)
org.antlr.grammar.v3.DefineGrammarItemsWalker.grammarSpec(DefineGrammarItemsWalker.java:572)
org.antlr.grammar.v3.DefineGrammarItemsWalker.grammar_(DefineGrammarItemsWalker.java:271)
org.antlr.tool.Grammar.defineGrammarSymbols(Grammar.java:791)
org.antlr.tool.CompositeGrammar.defineGrammarSymbols(CompositeGrammar.java:379)
org.antlr.Tool.process(Tool.java:484)
org.antlr.Tool.main(Tool.java:98)
:generateGrammarSource FAILED
```

cmd args

```
-o jconfig/build/generated-src/main/java
jconfig/src/main/antlr3/com/initvoid/jconfig/zconf/ZConf.g
jconfig/src/main/antlr3/com/initvoid/jconfig/zconf/ZConfHelpLexer.g
jconfig/src/main/antlr3/com/initvoid/jconfig/zconf/ZConfMainLexer.g
```

`'org.antlr:antlr:3.5.2'`

```
$ java -version
java version "1.8.0_11"
Java(TM) SE Runtime Environment (build 1.8.0_11-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.11-b03, mixed mode)
```

Grammar files: https://gist.github.com/166MMX/3c51992164f001db652a

Start by running the reported generateGrammarSource command with ZConf.g, ZConfHelpLexer.g, and ZConfMainLexer.g from the linked grammar files, using antlr 3.5.2. Trace the failure through Rule.trackRuleReferenceInAlt and the related grammar-processing stack; done means the grammars generate successfully without the ArrayIndexOutOfBoundsException.

Written by the indexing model from the issue text.