Moving the negative volume check into the geometry module

[Davknapp]

As @jmark mentioned in #751 we should also move the no-negative-volume check into the geometry module.

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[sandro-elsweijer]

We need a test for that

[sandro-elsweijer]

Did you forget to push the t8_geometry_zero.h?

[Davknapp]

Did you forget to push the t8_geometry_zero.h?

I don't think so? Is there anything missing?

[sandro-elsweijer]

Just one small thing