sprite plugin: do not check texture.image, it allows to used textures created by RenderTarget (#8619)

src/renderers/webgl/plugins/SpritePlugin.js

@@ -221,7 +221,7 @@ THREE.SpritePlugin = function ( renderer, sprites ) {
 			state.setDepthTest( material.depthTest );
 			state.setDepthWrite( material.depthWrite );
 
-			if ( material.map && material.map.image && material.map.image.width ) {
+			if ( material.map ) {
 
 				renderer.setTexture2D( material.map, 0 );