[llvm] [BOLT] Fix null pointer dereference in DWP processing with split DWARF (PR #191474)

[Farid Zakaria via llvm-commits]

fzakaria wrote:

@rafaelauler  thanks for writing that for me.
Writing lit tests are hard to see what to do.

Looks like that test with your changes fails appropriately.

```
--

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Failed Tests (2):
  BOLT :: X86/dwarf4-dwp-missing-line-contribution.s
  BOLT :: X86/dwarf4-dwp-x86.s


Testing Time: 8.05s

Total Discovered Tests: 682
  Skipped          :  26 (3.81%)
  Unsupported      :  27 (3.96%)
  Passed           : 626 (91.79%)
  Expectedly Failed:   1 (0.15%)
  Failed           :   2 (0.29%)

1 warning(s) in tests
FAILED: tools/bolt/test/CMakeFiles/check-bolt /home/fmzakari/llvm-build/tools/bolt/test/CMakeFiles/check-bolt
```

I reverted `X86/dwarf4-dwp-missing-line-contribution.s` accordingly. 

https://github.com/llvm/llvm-project/pull/191474