WebGLRenderer: Reset _currentGeometryGroupHash at the beginning of the frame.

src/renderers/WebGLRenderer.js

@@ -3352,6 +3352,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 		// reset caching for this frame
 
+		_currentGeometryGroupHash = - 1;
 		_currentMaterialId = - 1;
 		_currentCamera = null;
 		_lightsNeedUpdate = true;