fix(Visible): fix some errors when setting sheet.Instrument[i].Visible to false on multiple instruments.

src/MusicalScore/Graphical/MusicSheetCalculator.ts

@@ -1720,7 +1720,7 @@ export abstract class MusicSheetCalculator {
     protected maxInstrNameLabelLength(): number {
         let maxLabelLength: number = 0.0;
         for (const instrument of this.graphicalMusicSheet.ParentMusicSheet.Instruments) {
-            if (instrument.NameLabel.print && instrument.Voices.length > 0 && instrument.Voices[0].Visible) {
+            if (instrument.NameLabel?.print && instrument.Voices.length > 0 && instrument.Voices[0].Visible) {
                 let renderedLabel: Label = instrument.NameLabel;
                 if (!this.rules.RenderPartNames) {
                     renderedLabel = new Label("", renderedLabel.textAlignment, renderedLabel.font);

src/MusicalScore/Graphical/MusicSystemBuilder.ts

@@ -290,7 +290,7 @@ export class MusicSystemBuilder {
         const instruments: Instrument[] = this.graphicalMusicSheet.ParentMusicSheet.Instruments;
         for (let idx: number = 0, len: number = instruments.length; idx < len; ++idx) {
             const instrument: Instrument = instruments[idx];
-            if (instrument.Voices.length === 0 || !instrument.Visible) {
+            if (!instrument.Visible || instrument.Voices.length === 0) {
                 continue;
             }
             for (let idx2: number = 0, len2: number = instrument.Staves.length; idx2 < len2; ++idx2) {