Make the code in scanner/groovy.rb robust.

[junaruga]

Fix small issues for lib/coderay/scanners/groovy.rb.

inline_block_paren_depth is initialized as nil.
But the code inline_block_paren_depth += 1, inline_block_paren_depth -= 1, inline_block_paren_depth == 0 has a possibility to raise unintended NoMethodError.
It looks good to initialize inline_block_paren_depth is initialized as 0 or add checks before the codes.

2. string_delimiter can be nil as a possibility. Adding checks looks better.

[junaruga]

This report is by a static code analysis tool in our company (Maybe Coverity Scan).

[korny]

Mmh. I don’t think there’s really a bug here, since I never got an error with the current version even with thorough testing (see the scanner test suite). While I agree with the first change, the second one would slow down the scanner. I don’t think we need such checks unless someone can actually produce an error here :)

[junaruga]

Sure, @korny . I respect your decision. It's up to you.