asn: fix coverity null deref warnings.

[philljj]

Description

Fix coverity issues in wolfcrypt/src/asn.c.

[Copilot]

Pull request overview

Resolves Coverity-reported null dereference warnings in wolfcrypt/src/asn.c by preventing macro argument evaluation when key pointers are invalid and making cleanup paths safer.

Changes:

• Guard ALLOC_ASNGETDATA / CALLOC_ASNGETDATA invocations behind ret == 0 to avoid dereferencing key->heap when key is invalid.
• Make FREE_ASNSETDATA cleanup resilient to key == NULL using a conditional heap argument.

Comments suppressed due to low confidence (4)

wolfcrypt/src/asn.c:1

• Optional: instead of introducing an extra if (ret == 0) block solely to avoid evaluating key->heap, consider passing a safely-evaluated heap expression into the macro (e.g., key ? key->heap : NULL). This keeps control flow flatter and relies on the existing ret-based gating inside the macro (if present), while still preventing null deref from macro argument evaluation.
  wolfcrypt/src/asn.c:1
• Optional: same pattern as earlier—if the only reason for the if (ret == 0) wrapper is to avoid evaluating key->heap in macro arguments, a conditional heap expression argument can avoid added nesting while still being null-safe.
  wolfcrypt/src/asn.c:1
• Please confirm FREE_ASNSETDATA is defined to safely accept a NULL heap and still free using the correct allocator. If the heap parameter controls which allocator is used, passing NULL could risk mismatched free behavior. A more robust approach is to capture the heap used for allocation into a local variable (or only call the free macro when the allocator context is known) and use that consistently during cleanup.
  wolfcrypt/src/asn.c:1
• Same concern as the earlier FREE_ASNSETDATA change: if heap selects the allocator, ensure NULL is a supported value that won’t cause allocator mismatch. Consider retaining the allocation heap in a local variable for consistent cleanup.

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[philljj]

Retest this please.