Fix issue #1498 - release the GIL
Fix issue #1498 - release the GIL

This was odd, thanks to Chris for pointing out the temporary release of
the Python GIL which seems to address the issue in the testing I did.

mathturtle/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz