fix(importer): use explicit bounds check for masterBars access

The previous masterBar lookup used `score.masterBars[barNumber]` with
an `| undefined` type and an `if (!masterBar)` guard. That relies on
JS array out-of-bounds returning undefined — not C# / Kotlin
transpilation compatible, since the indexed access there throws
IndexOutOfRangeException / IndexOutOfBoundsException before the
undefined-check has a chance to run.

Replace with an explicit `barNumber < 0 || barNumber >= length` guard
before the access, matching the idiom already used 9 lines above for
sustain-pedal markers (GpifParser.ts) and in Gp3To5Importer.ts:508.

Addresses review feedback from @Danielku15 on PR #2668.

Author: kaizenman

packages/alphatab/src/importer/GpifParser.ts

@@ -2892,11 +2892,11 @@ export class GpifParser {
 
         // build masterbar automations
         for (const [barNumber, automations] of this._masterTrackAutomations) {
-            const masterBar: MasterBar | undefined = this.score.masterBars[barNumber];
-            if (!masterBar) {
+            if (barNumber < 0 || barNumber >= this.score.masterBars.length) {
                 // automation references a bar that is not in the score's masterBars list
                 continue;
             }
+            const masterBar: MasterBar = this.score.masterBars[barNumber];
             for (let i: number = 0, j: number = automations.length; i < j; i++) {
                 const automation: Automation = automations[i];
                 switch (automation.type) {