Bug Fix: Add safe LVGL object deletion to prevent LoadProhibited crashes

[Stuckya]

I was encountering intermittent crashes when my kids were using the remote. This led me to debugging the crashes and I uncovered 3 issues along the way. This was the 2nd issue.

Problem:

LoadProhibited crash with EXCVADDR: 0x00000009 when pressing KEY_RIGHT repeatedly in default scene, caused by invalid LVGL object access during GUI navigation.

Root Cause:

• setActiveTab() function called LVGL functions on potentially NULL or invalid tabview objects.
• clear_tabview() and clear_panel() deleted objects without validation.
• Possible race conditions between object deletion and usage.

Fix:

1. Added safe_delete_lv_obj() helper function to validate objects before deletion.
2. Added null and validity checks in setActiveTab() before using tabview.
3. Refactored clear_tabview() and clear_panel() to use safe deletion with early returns.
4. Prevents LoadProhibited crashes from invalid LVGL object access.