Bad end-of-string check in get_next_token (CID various)

There's a coverity warning about an overflow in test_parsecommmon. I think it is happening because of this code:

 *s + 16 >= eol

That's the wrong way to test for end-of-string, since C says that *s+16 is undefined behavior if the resulting pointer would be more than 1 off the end of the allocated byte array.