fix zero metalness appearance
fix zero metalness appearance

RainsSoft/engine,SuperStarPL/engine,guycalledfrank/engine,nizihabi/engine,RainsSoft/engine,MicroWorldwide/PlayCanvas,playcanvas/engine,3DGEOM/engine,3DGEOM/engine,maxwellalive/engine,horryq/engine-1,shinate/engine,H1Gdev/engine,sanyaade-teachings/engine,maxwellalive/engine,sanyaade-teachings/engine,SuperStarPL/engine,horryq/engine-1,shinate/engine,sanyaade-teachings/engine,MicroWorldwide/PlayCanvas,maxwellalive/engine,H1Gdev/engine,RainsSoft/engine,aidinabedi/playcanvas-engine,sereepap2029/playcanvas,aidinabedi/playcanvas-engine,sereepap2029/playcanvas,nizihabi/engine,SuperStarPL/engine,shinate/engine,sereepap2029/playcanvas,guycalledfrank/engine,3DGEOM/engine,nizihabi/engine,horryq/engine-1,playcanvas/engine