Russia main.cpp holes_inside_polygons() bug

[fillingthemoon]

I came across a bug on the master branch.

To reproduce this bug, please follow these steps:

1. git checkout master

2. Place the attached russia.geojson (after unzipping) and inset_russia_population.csv into the sample_data/inset_data/ directory.
   inset_russia_modified_population.csv
   russia.geojson.zip

3. Run the following in your terminal.

cd build/
cmake .
make
./cartogram -g ../sample_data/inset_data/russia.geojson -v ../sample_data/inset_data/inset_russia_population.csv

4. Issue: It prints a bunch of coordinates to the output (screenshot below) and does not produce any GeoJSONs. When I comment out lines 190-201 in main.cpp, however, it runs fine. It seems then that this Russia example is getting stuck in holes_inside_polygons().

[mgastner]

Exterior ring and hole shared a common vertex. Updated versions of the C++ code do not treat this as a topology error any longer.