fix(settings): keep the stored port when a port field is cleared (#6121)

* fix(settings): keep the stored port when a port field is cleared

Clearing the panel-port, subscription-port or LDAP-port InputNumber
fired onChange(null), which the handlers coerced to 0; on blur Ant
Design clamped the empty field to min=1 and the next save silently
persisted port 1. For subPort that breaks the generated subscription
links; for webPort it moves the panel itself to port 1 and locks the
admin out until the port is fixed via the x-ui CLI.

Ignore null changes so clearing a port field snaps back to the last
valid value instead of committing a bogus port.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* test(settings): pin cleared port fields to the stored value

Clearing the subscription-port field must not reach updateSetting at
all, while typed ports still pass through unchanged. Pins the fix so a
handler refactor cannot silently reintroduce the clamped port 1.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

frontend/src/test/subscription-general-tab.test.tsx

@@ -12,6 +12,36 @@ function LocationProbe() {
 }
 
 describe('SubscriptionGeneralTab', () => {
+  it('keeps the stored subscription port when the field is cleared', () => {
+    const updateSetting = vi.fn();
+
+    renderWithProviders(
+      <MemoryRouter initialEntries={['/settings#subscription']}>
+        <SubscriptionGeneralTab allSetting={new AllSetting({ subPort: 2096 })} updateSetting={updateSetting} />
+      </MemoryRouter>,
+    );
+
+    const portInput = screen.getByDisplayValue('2096');
+    fireEvent.change(portInput, { target: { value: '' } });
+    fireEvent.blur(portInput);
+
+    expect(updateSetting).not.toHaveBeenCalled();
+  });
+
+  it('forwards typed subscription ports unchanged', () => {
+    const updateSetting = vi.fn();
+
+    renderWithProviders(
+      <MemoryRouter initialEntries={['/settings#subscription']}>
+        <SubscriptionGeneralTab allSetting={new AllSetting({ subPort: 2096 })} updateSetting={updateSetting} />
+      </MemoryRouter>,
+    );
+
+    fireEvent.change(screen.getByDisplayValue('2096'), { target: { value: '8443' } });
+
+    expect(updateSetting).toHaveBeenCalledWith({ subPort: 8443 });
+  });
+
   it('uses router navigation to open subscription format settings', () => {
     const allSetting = new AllSetting({ subClashEnable: true });