Text material is set only after font is loaded

currently the material is set after the font is loaded. This leads to a crash in threejs where the vertexshader is undefined.
This was crashing Zethus when adding a Tf view.

The fix is to assign the material before the callback.

We have a fix in our master branch: https://github.com/rapyuta-robotics/amphion/compare/devel...RoboStack:master

Do you guys still work on Amphion & Zethus?