[Bug] - Plots are useless when height is below zero

[straussi]

When creating Plots in Germany (CubicChunks 1.12.2), f.e. in the cities Oldenburg or Rostock near the sea, heights of some blocks inside the selection might fall below zero. However, you can create plots normally, but when it comes to users wanting to build on that plots, it gives the error message "Unexpected error whilst creating plot. Please try again later".
Because that "blocks" whole plot-cities, when only one plot has only one block in the selection with height <0 that issue is really frustrating for users. We hope you can fix that.