[1c] Fix native code bugs in ARimageFsetDisplay.cpp (NULL deref, exit(), memory leaks, pointer truncation)

[kalwalt]

Summary

Fix multiple native-code bugs and unsafe patterns in emscripten/ARimageFsetDisplay.cpp

Environment

• Product/Service: FeatureSET-Display — Emscripten/wasm native layer
• File: emscripten/ARimageFsetDisplay.cpp

Problem Description

Several distinct bugs and unsafe patterns exist in the native C++ layer:

1. NULL-pointer dereference (lines 109–128): loadNFTMarker logs an error when ar2ReadSurfaceSet returns NULL but continues execution, then dereferences the null pointer.
2. exit() terminates the wasm runtime (lines 148, 154): exit(0) / exit(-1) on file errors tear down the entire wasm runtime in the browser instead of returning an error code to JS.
3. Memory leak in setup(): setup() mallocs imgBW with width*height*4, but loadNFTMarker later overwrites the pointer with surfaceSet[...]->imgBW — the original malloc'd buffer leaks. A second malloc based on uninitialized num_F_points_NFT also leaks.
4. Pointer truncation in log statements: ARLOGi("...%d", arc->imgBW) and (int)arc->imgBW truncate 64-bit pointers — use %p / uintptr_t.
5. Bounds check after write (line 153): The if (surfaceSetCount == PAGES_MAX) exit(-1) guard fires after the array has already been written; the check must be reordered to precede the write.

Expected Behavior

• loadNFTMarker returns an error code when ar2ReadSurfaceSet returns NULL; execution does not continue.
• File errors return error codes to JS instead of calling exit().
• No memory leaks in setup() or loadNFTMarker.
• Pointer values logged correctly with %p / uintptr_t.
• Bounds check occurs before writing to the array.

Actual Behavior

• NULL dereference crash possible after a failed surface-set load.
• exit() calls kill the wasm module on file errors, breaking the page.
• imgBW malloc leak on every loadNFTMarker call.
• Pointer values silently truncated in logs on 64-bit targets.
• Out-of-bounds array write possible before the PAGES_MAX guard triggers.

Tasks

• Guard loadNFTMarker against NULL return from ar2ReadSurfaceSet and return an error code
• Replace exit(0) / exit(-1) with proper error-code returns (lines 148, 154)
• Free the original imgBW malloc before overwriting the pointer in loadNFTMarker; audit the num_F_points_NFT-based malloc
• Fix ARLOGi calls to use %p / (uintptr_t)arc->imgBW
• Reorder the PAGES_MAX bounds check to occur before the array write

Impact

High — NULL dereference and exit() calls are crash/runtime-termination bugs. Memory leaks compound on repeated marker loads.

Additional Context

These fixes pair naturally with rebuilding the wasm binary anyway (see issue 3b — toolchain refresh). Fixing exit() calls is a prerequisite for any production use in a browser tab.