DRG-13307: off =string and len =string references character past end-of-file of string character document, at line string

DRG-13307: off =string and len =string references character past end-of-file of string character document, at line string

Cause: value of off attribute plus value of len attribute is greater than the number of characters in the document

Action: modify user-defined lexer index procedure to return valid values for off and len attributes