[GeoLib] Corrected implementation of check if Polyline is in Polygon.

The check if a polyline is in a polygon is needed within the SimplePolygonTree.
```pnt_vec``` is a ```GeoLib::PointVec``` object. The method ```push_back(GeoLib::Point*)``` returns the id/position of the "push backed" point within the ```PointVec``` object. If the given point is already included in the vector, the point will be destroyed and the id of the existing point will be returned. I see that the name is a bit misleading.