[llvm] [SelectionDAG] Fix null pointer dereference in resolveDanglingDebugInfo (PR #180425)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

I suggest you move everything below the main PR description (i.e., after the `---` in markdown) to a comment so that it is not included in the final commit message. 

https://github.com/llvm/llvm-project/pull/180425