Re-enabling theming requires two restarts instead of one #4503

After disabling theming and restarting, if the user re-checks Enable Theming and clicks Apply, Eclipse restarts. After that restart theming is active but no theme has been selected or applied. The user must open Preferences a second time, pick a theme, and restart again. Two restarts are required to get back to a themed state.

Steps to reproduce

From a fresh installation and clean workspace:

1. Open Window → Preferences → General → Appearance with theming enabled.
2. Uncheck Enable Theming, click Apply, and restart when prompted.
3. After restart, open Window → Preferences → General → Appearance.
4. Re-check Enable Theming, click Apply, and restart when prompted.
5. Current Beha: Eclipse starts with theming on but no theme applied — the workbench has no CSS styling. User must open Preferences again, select a theme, and restart a third time.
6. Expected: After step 4's restart, Eclipse starts with theming on and a theme already applied — one restart total.

Follow up to Issue: #4502

Tested under this environment:

Eclipse SDK
Version: 2026-12 (4.42)
Build id: I20261015-2300
OS: Mac OS X, v.27.0.1, aarch64 / cocoa
Java vendor: IBM Corporation
Java runtime version: 26.0.1+8