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

[Jonas Devlieghere via llvm-commits]

JDevlieghere wrote:

> I can add a unit-test similar to how I did in #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

For small inputs, unit tests and obj2yaml tests (as @sbc100 suggested) are great options. When the fuzzer generated inputs are large then you'll either want to reduce the test case or try to craft something smaller that exhibits the same issue. 

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