LibJS: Fix crashing exception in Value::ordinary_has_instance()

Two issues:

- throw_exception() with ErrorType::InstanceOfOperatorBadPrototype would
  receive rhs_prototype.to_string_without_side_effects(), which would
  ASSERT_NOT_REACHED() as to_string_without_side_effects() must not be
  called on an empty value. It should (and now does) receive the RHS
  value instead as the message is "'prototype' property of {} is not an
  object".
- Value::instance_of() was missing an exception check after calling
  has_instance_method, to_boolean() on an empty value result would crash
  as well.

Fixes #3930.

Libraries/LibJS/Tests/operators/instanceof-basic.js

@@ -22,3 +22,15 @@ test("derived ES5 classes", () => {
     expect(d instanceof Derived).toBeTrue();
     expect(d instanceof Base).toBeTrue();
 });
+
+test("issue #3930, instanceof on arrow function", () => {
+    function f() {}
+    const a = () => {};
+
+    expect(() => {
+        f instanceof a;
+    }).toThrow(TypeError);
+    expect(() => {
+        a instanceof a;
+    }).toThrow(TypeError);
+});