[relate] Fix L/L : handling of MLs containing overlapping, collinear Linestrings.

It's also consistent with the behavior for Point-like Linestrings.

E.g. some MultiLinestring may have boundary and interior in the same point:

Ls1:
  |--------------|
MLs2:
  |------------|
|------|

In this case the current version of the algorithm will set BB=0 and BI=0.