Bugs with pattern guessing

[ghost]

Currently pattern guessing can place an N match at the end of a clip, and still allows "ccnnb" match sequences with "use ccnnn" disabled.

[myrsloik]

Impossible matches are now prevented at start and end.
According to the code you can have b matches with all patterns, ccnnc included, which will then be indistinguishable from ccnnn. If anything I think the correct solution is a checkbox to decide if b matches are to be tried at all. In short: I don't know how you expect this to change