RFR: 8353440: Disable FTP fallback for non-local file URLs by default

[Eirik Bjørsnøs]

On Tue, 15 Apr 2025 20:09:39 GMT, Eirik Bjørsnøs <eirbjo at openjdk.org> wrote:

> The current behavior for _existing_ UNC paths would be unaffected by this change.

For the sake of completeness: 

If `Files::exists` failed for a UNC path before this change, then the code would continue to the FTP fallback and the result would depend on whether a public anonymous FTP server was available on the non-local host. 

After this change, when a UNC path does not exist, then the connection will fail with a `MalformedURLException`, just like the Unix implementation.

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PR Comment: https://git.openjdk.org/jdk/pull/24657#issuecomment-2807431756