make DTE.GetActiveDocument safe
fixed: SyntaxConstructClassifier passes wrong file path to LanguageService
cleanup
do not raise exception in SyntaxConstructorClassifierProvider in case there is no active document

remove exception catching in DTE.GetActiveDocument
Merge pull request #232 from vasily-kirichenko/fix-colorizer-uses-wrong-doc

Fixed: SyntaxConstructClassifier passes wrong file path to Checker