WebGLBackground: respect autoClear in AR (#26428)

src/renderers/webgl/WebGLBackground.js

@@ -44,24 +44,15 @@ function WebGLBackground( renderer, cubemaps, cubeuvmaps, state, objects, alpha,
 
 		}
 
-		const xr = renderer.xr;
-		const environmentBlendMode = xr.getEnvironmentBlendMode();
+		const environmentBlendMode = renderer.xr.getEnvironmentBlendMode();
 
-		switch ( environmentBlendMode ) {
+		if ( environmentBlendMode === 'additive' ) {
 
-			case 'opaque':
-				forceClear = true;
-				break;
+			state.buffers.color.setClear( 0, 0, 0, 1, premultipliedAlpha );
 
-			case 'additive':
-				state.buffers.color.setClear( 0, 0, 0, 1, premultipliedAlpha );
-				forceClear = true;
-				break;
+		} else if ( environmentBlendMode === 'alpha-blend' ) {
 
-			case 'alpha-blend':
-				state.buffers.color.setClear( 0, 0, 0, 0, premultipliedAlpha );
-				forceClear = true;
-				break;
+			state.buffers.color.setClear( 0, 0, 0, 0, premultipliedAlpha );
 
 		}