Crash scanning a map with no map name on non-Windows builds

[bobtista]

Prerequisites

• I have searched for similar issues and confirmed this is not a duplicate

Game Version

• Command & Conquer Generals
• Command & Conquer Generals: Zero Hour

Bug Description

On non-Windows builds the game crashes while building the map cache, on the first map whose world dictionary has no map name.

Reproduction Steps

1. Place a map with no map name in its world dictionary into the user maps directory on a non-Windows build.
2. Start the game so the map cache scans the directory.
3. Observe the crash while the cache is being built.

Additional Context

The fallback that derives a display name searches the file name for the Windows separator and adds one to the result without checking it, so on other platforms a null pointer reaches AsciiString::set.