copyPds: Misssing source PDS throws a non-user-friendly error

[zFernand0]

Found this issue while testing, but this also on the master branch

> zdev files copy ds DS.DOES.NOT.EXIST fernando.test.pds.small      [±truncate-lrecl-target ✓(✹)]
Unable to perform this operation due to the following problem.
Cannot read properties of undefined (reading 'dsorg')

Response From Service
TypeError: Cannot read properties of undefined (reading 'dsorg')

I believe we will need to handle missing datasets in the isPDS function, and maybe fail a bit more gracefully 🙏

Originally posted by @zFernand0 in #2433 (comment)

[github-actions]

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