GeoJSON: Add warn message when save a geotable with incorrect CRS

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.72%. Comparing base (f633aa3) to head (71a67cf). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #97 +/- ## ======================================= Coverage 94.71% 94.72% ======================================= Files 17 17 Lines 1078 1080 +2 ======================================= + Hits 1021 1023 +2 Misses 57 57 ```

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