Exportation fails

[Blackcatn13]

Exportation fails when mesh have non consecutive material id.

[Blackcatn13]

Exportation with the new exporter and without material don't crash.
If after testing the new exporter with material the crash is not present, the new export is going to move as the must use version, and the old is going to be deprecated.

[Blackcatn13]

The bug is still present in the new exporter, if no material is applied work's fine.