Android: don't start the game thread twice when recreated during setup

[skwidge]

Fixes a crash on first launch, found while taking store screenshots in the emulator.

Cause. On first launch the assets are copied in an AsyncTask. If the activity is recreated during the copy (for example by a dark mode or wallpaper colour change, which aren't in configChanges), onDestroy replaces the static NH_State and the new activity starts a second copy. Both copies then call startNetHack on the new state, and the second Thread.start() throws IllegalThreadStateException.

Fix. Each copy remembers the NH_State it was started for and only starts the game if that state is still current. The copies run serially (AsyncTask.execute), so they never write the files concurrently.

Testing (Android 14 emulator, pm clear, launch with am start -W, then cmd uimode night yes during the copy):

• Before: crashed 6/6 runs with IllegalThreadStateException at NetHackIO.start.
• After: 0 crashes in 7 runs; the game starts after the relaunch and a new game plays normally.
• A plain first launch without recreation still reaches "Who are you?".
• gradlew build (with lint) passes.

No version bump here, to avoid conflicting with #7 (3.6.7-6).

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