make addDefaultMaterials an explicit call

Author: Floppy

examples/jsm/loaders/LDrawLoader.js

@@ -1907,7 +1907,7 @@ class LDrawLoader extends Loader {
 		fileLoader.load( url, text => {
 
 			// Initializes the materials library with default materials
-			this.addMaterials( [] );
+			this.addDefaultMaterials();
 
 			this.partsCache
 				.parseModel( text )
@@ -1966,6 +1966,12 @@ class LDrawLoader extends Loader {
 
 		}
 
+		return this;
+
+	}
+
+	addDefaultMaterials() {
+
 		// Add default main triangle and line edge materials (used in pieces that can be colored with a main color)
 		this.addMaterial( this.parseColorMetaDirective( new LineParser( 'Main_Colour CODE 16 VALUE #FF8080 EDGE #333333' ) ) );
 		this.addMaterial( this.parseColorMetaDirective( new LineParser( 'Edge_Colour CODE 24 VALUE #A0A0A0 EDGE #333333' ) ) );