cache result (#28553)

Co-authored-by: aardgoose <[email protected]>

examples/jsm/renderers/webgl/utils/WebGLExtensions.js

@@ -19,6 +19,8 @@ class WebGLExtensions {
 
 			extension = this.gl.getExtension( name );
 
+			this.extensions[ name ] = extension;
+
 		}
 
 		return extension;