[llvm] [WasmObjectFile] fix NULL-dereference (PR #77708)

[via llvm-commits]

DavidKorczynski wrote:

How would you like the test? In essence the OSS-Fuzz set up is a test: compile the fuzzer and run the reproducer case against the reproducer file in https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30789

I can add a unit-test similar to how I did in https://github.com/llvm/llvm-project/pull/76676 but am not sure if this is the desired approach for all fuzzing results? Please confirm if you'd like this and I'll add one

https://github.com/llvm/llvm-project/pull/77708