[llvm] [Metadata] Return the valid DebugLoc if one of them is null with -pick-merged-source-locations. (PR #138148)

[Snehasish Kumar via llvm-commits]

snehasish wrote:

### Merge activity

* **May 2, 12:35 PM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/138148).


https://github.com/llvm/llvm-project/pull/138148