bug#52337: 27.2; Doc string of `dired-check-process'

[Drew Adams]

1. Please consider filling the third sentence ("On error,...").

2. The "Else returns nil for success." isn't too clear.  Please consider
making it more clear that the return value is nil for success and either
ARGUMENTS or PROGRAM for failure.

It's also not clear under what conditions, or when, ARGUMENTS is
returned or PROGRAM is returned.  "Offending" doesn't help in that
regard.  Is it possible for both ARGUMENTS and PROGRAM to "offend"?

In GNU Emacs 27.2 (build 1, x86_64-w64-mingw32)
 of 2021-03-26 built on CIRROCUMULUS
Repository revision: deef5efafb70f4b171265b896505b92b6eef24e6
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.19042
System Description: Microsoft Windows 10 Pro (v10.0.2009.19042.1348)

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