This occurred when the null term was reached - the token was freed, but
no error was thrown (it's just the end of the string), so the program
attempted to increment the index using freed token data.
The code is limited in two aspects, at the moment:
* It's not very well tested
* The current "best" match is just the one that occurred last. While
this is just fine in terms of length, this leaves open to chance which
pattern type will be returned if multiple patterns of the same length
match.
