FIX: NavArea::ComputeApproachAreas() hang during *.nav file generation

[SergeyShorokhov]

Thanks to @CH3L74 for finding the bug on zm_flood map

video: https://youtu.be/Lu0yzVpQoAE

P.S: Very Sleepy software helps to find where is a bug http://www.codersnotes.com/sleepy/

Fix Hang on *.nav Generating in CNavArea::ComputeApproachAreas()

Description

This PR fixes a hanging issue encountered during the generation of *.nav files in the CNavArea::ComputeApproachAreas() function. The problem occurred when the approach areas were being computed, causing the process to freeze under certain conditions.

Changes:

• Optimized the approach area computation by handling edge cases where areas could not be reached or were blocked.
• Added additional checks to prevent infinite loops and overflow while building paths to distant areas.
• Refactored pathfinding logic to ensure smooth enumeration of approach areas without causing performance issues or hangs.

Issue:

• Hang during approach area computation: The function would enter an infinite loop or block during pathfinding when certain areas were not reachable.

Fixes:

• Improved pathfinding efficiency and added safety checks to prevent pathfinding failures from affecting subsequent computations.

This fix should resolve the hang issue and improve the reliability of the navigation area generation process.