Fixed indexing error that was caused when the prefix_length is greater than the length of the list of tokens. This would happen when the token list was empty.
Coverage remained the same at 73.061% when pulling 2faff6ad9c635f9fd9bda0954aebca3729dd7c27 on bug_appveyor into c446c6269b4cdce25d142ff6bfecef23f33a6718 on master.
Fixed indexing error that was caused when the prefix_length is greater than the length of the list of tokens. This would happen when the token list was empty.