set boolean to `currentPremultipledAlpha` (#24955)

src/renderers/webgl/WebGLState.js

@@ -718,7 +718,7 @@ function WebGLState( gl, extensions, capabilities ) {
 		}
 
 		currentBlending = blending;
-		currentPremultipledAlpha = null;
+		currentPremultipledAlpha = false;
 
 	}