chore: ensure key exists so that bootstrapping works

Author: JairusSW

src/compiler.ts

@@ -7362,8 +7362,9 @@ export class Compiler extends DiagnosticEmitter {
     let resolver = this.resolver;
     let target = resolver.lookupExpression(targetExpression, this.currentFlow, Type.auto, ReportMode.Swallow);
     if (target && target.kind == ElementKind.Local) {
-      let tupleLocals = this.tupleLocalComponents.get(<Local>target);
-      if (tupleLocals) {
+      let targetLocal = <Local>target;
+      if (this.tupleLocalComponents.has(targetLocal)) {
+        let tupleLocals = assert(this.tupleLocalComponents.get(targetLocal));
         let index = resolver.resolveTupleElementLiteralIndex(
           expression.elementExpression,
           tupleLocals.length,