Fixed narrowing in case clauses that follow other clauses that return (#56358)

src/compiler/binder.ts

@@ -1689,9 +1689,13 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
         const clauses = node.clauses;
         const isNarrowingSwitch = node.parent.expression.kind === SyntaxKind.TrueKeyword || isNarrowingExpression(node.parent.expression);
         let fallthroughFlow = unreachableFlow;
+
         for (let i = 0; i < clauses.length; i++) {
             const clauseStart = i;
             while (!clauses[i].statements.length && i + 1 < clauses.length) {
+                if (fallthroughFlow === unreachableFlow) {
+                    currentFlow = preSwitchCaseFlow!;
+                }
                 bind(clauses[i]);
                 i++;
             }