fix heightmap without normals (#963)
fix heightmap without normals (#963)


guycalledfrank/engine,playcanvas/engine,H1Gdev/engine,MicroWorldwide/PlayCanvas,MicroWorldwide/PlayCanvas,guycalledfrank/engine,sereepap2029/playcanvas,H1Gdev/engine,sereepap2029/playcanvas,playcanvas/engine,aidinabedi/playcanvas-engine,aidinabedi/playcanvas-engine,sereepap2029/playcanvas