[pct]: * Avoid "Cannot take substr outside string" error when an interactive-mode   program throws an exception that doesn't have a message (e.g., exit 0) * Resolves RT#50552.
[pct]:
* Avoid "Cannot take substr outside string" error when an interactive-mode
  program throws an exception that doesn't have a message (e.g., exit 0)
* Resolves RT#50552.


git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@25570 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

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