[llvm] [MsgPack] Return an Error instead of bool from readFromBlob (PR #74357)

[Scott Linder via llvm-commits]

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@@ -424,7 +424,7 @@ class Document {
   /// map entry, a nil node otherwise.
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slinder1 wrote:

I'm not sure how to leave a comment in the context above, but the doc-comment still mentions `Returns false if...`

https://github.com/llvm/llvm-project/pull/74357