Remove lines with length of zero from grid

[gplssm]

Simple approach on that:

• If a line has length of zero, don't add to the database table
• remove isolated bus and replace by the bus on the other side

Maybe it's wise to do this within Dingo

[gplssm]

This is maybe not required anymore if LoadAreaCenter load is responsible for this error by being added with line length of zero.

1. Check if LoadAreaCenter is responsible
2. If some, solve it in a different way. If not, have a clever idea!

[gplssm]

This is now handled in dingo as lines with length 0m are treated as invalid input