WebGLTextures: Make .clampToMaxSize() more robust

[Mugen87]

see #13454

[mrdoob]

I would do this instead:

function clampToMaxSize( image, maxSize ) {

	if ( image.width > maxSize || image.height > maxSize ) {

		if ( 'data' in image ) {

			console.warn( 'THREE.WebGLRenderer: image in DataTexture is too big (' + image.width + 'x' + image.height + ').' );
			return;

		}

		// Warning: Scaling through the canvas will only work with images that use
		// premultiplied alpha.

[mrdoob]

Thanks!