LibJS: Avoid emptying the return value register in try/finally

This works because at the end of the finally chunk, a
ContinuePendingUnwind is generated which copies the saved return value
register into the return value register. In cases where
ContinuePendingUnwind is not generated such as when there is a break
statement in the finally block, the fonction will return undefined which
is consistent with V8 and SpiderMonkey.

Libraries/LibJS/Tests/try-finally-break.js

@@ -490,3 +490,17 @@ test("Break with nested mixed try-catch/finally", () => {
 
     expect(executionOrder).toEqual([1, 2]);
 });
+
+test("Break in finally return in try", () => {
+    function foo() {
+        do {
+            try {
+                return "bar";
+            } finally {
+                break;
+            }
+        } while (expect.fail("Continued after do-while loop"));
+    }
+
+    expect(foo()).toEqual(undefined);
+});