SI-7039 if unapplySeq returns an option of a product `nbSubPats` is not ...

...enough to check because this will miss a pattern with one product element and an empty repeated argument list.

The proposed solution is to check the number of elements in the expected product as well before concluding that an extractor is _no_ unapplySeq.

This seems to fix it but I suppose there are better ways to achieve the same effect.