fix the measure number label.SVGNode not being set in osmd-extended, unlike in public osmd (#1479)

see https://github.com/opensheetmusicdisplay/opensheetmusicdisplay/discussions/1479

this was working in public osmd, but not in the audio player.

src/MusicalScore/Graphical/MusicSheetDrawer.ts

@@ -156,7 +156,7 @@ export abstract class MusicSheetDrawer {
         }
         const calcResults: LabelRenderSpecs = this.calculateLabel(graphicalLabel);
 
-        this.renderLabel(graphicalLabel, layer, calcResults);
+        return this.renderLabel(graphicalLabel, layer, calcResults);
     }
 
     protected calculateLabel(graphicalLabel: GraphicalLabel): LabelRenderSpecs {