Flood Fill and infeasible situations

[jara001]

Again, as another by-product of Curvature2 selector, a "bad" behaviour of Flood Fill was detected.
Here, the "bad" is properly chosen, as it is not entirely segmentator's fault.

When a group center is selected in the unreachable area, Flood Fill is unable to inflate it, resulting in zero-length segment. This segment causes problems in other parts, e.g., plotting, as we are passing empty list (array) to places that do not expect this.

I suggest to add new parameter to Flood Fill that would make it possible to inflate also these group centers, however it a slightly different manner -- to make sure that is is also used.

One of the possible problems might be splitting the segment into two parts.