[3.12] gh-102541: Fix Helper.help("mod") for non-existent mod (GH-105934) (#106322)

gh-102541: Fix Helper.help("mod") for non-existent mod (GH-105934)

If the output arg to Helper() is a stream rather than the default None, which means 'page to stdout', the ImportError from pydoc.resolve is currently not caught in pydoc.doc. The same error is caught when output is None.
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(cherry picked from commit 0530f4f64629ff97f3feb7524da0833b9535e8b6)

Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>