RFR: 8349369: test/docs/jdk/javadoc/doccheck/checks/jdkCheckLinks.java did not report on missing man page files

[Nizar Benalla]

On Tue, 4 Feb 2025 14:39:49 GMT, Nizar Benalla <nbenalla at openjdk.org> wrote:

> Please review this small update to make the test more robust, the test did not always check links to other files if they did not contain a fragment or a `#`symbol.
> 
> I'd like to add that the original [doccheck](https://github.com/openjdk/doccheck) also didn't pick up on these missing files when I ran it. 
> 
> TIA

I made improvements based on the review feedback, the test now catches missing files.

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PR Comment: https://git.openjdk.org/jdk/pull/23441#issuecomment-2940406233