em-extpipe: Catch eshell-incomplete thrown while parsing

em-extpipe: Catch eshell-incomplete thrown while parsing

* lisp/eshell/em-extpipe.el (em-extpipe--or-with-catch): New macro.
(eshell-parse-external-pipeline): Use new macro to treat
`eshell-incomplete' as a failure of the parse function to move us
forward (Bug#54603).  Thanks to Jim Porter <jporterbugs@gmail.com> for
the report and for help isolating the problem.

* test/lisp/eshell/eshell-tests.el
(eshell-test/lisp-command-with-quote): New test for Bug#54603, thanks
to Jim Porter <jporterbugs@gmail.com> (bug#54603).