[llvm-objdump][MachO] Correctly handle the llvm::Error when -dsym has errors

In an assert build, the Error gets destroyed and we get "Program aborted
due to an unhandled Error:".

In release, we get an empty message.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350848 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed