Incorrect geometry for Multipolygons with shells which share a single point

[rtroilo]

This PR is for working on issue #424. Wrong geometry generation for multipolygon where shells share a common node.

   lat
    ^
    4 a--d
    3 |  |
    2 b--c--e
    1    |  |
    0    g--f
      0123456 -> lon
  
   A: (a,b,c)\
              one shell (a,b,c,d,a)
   B: (c,d,a)/
  
   C: (c,e,f)\
              one shell (c,e,f,g,c)
   D: (f,g,c)/

Corresponding issue

Closes #424

Checklist

• [x] My code follows the code-style rules, and I have checked on the static analyses and benchmark (if applicable) results
• [x] I have commented my code
• [x] I have written javadoc (required for public classes and methods)
• [x] I have added sufficient unit tests
• ~~I have made corresponding changes to the documentation~~
• [x] I have updated the CHANGELOG.md
• ~~I have adjusted the examples or created an issue in the corresponding repository~~
• ~~I have adjusted the benchmark or created an issue in the corresponding repository~~