Displaying PDF files from an external URL can fail sometimes

[aubincleme]

Steps to reproudce :

• Install the PDF Viewer macro in version 2.5.3 on a standard XWiki 15.10.x
• In a page, add the following content :

  
  {{pdfviewer file="http://dev.xwiki.org/xwiki/bin/download/GoogleSummerOfCode/gsoc.pdf" /}}

{{pdfviewer file="https://www.dfn.de/wp-content/uploads/2021/12/satzungdfn.pdf"/}}

* Save and view

You should get a result similar to the following :

![image](https://github.com/xwikisas/macro-pdfviewer/assets/5938943/5d2cfdc6-3ad7-40b4-a4af-6da24a256815)

This issue targets only the result produced by the first `pdfviewer` macro, pointing to `gsoc.pdf`. For some reason, the PDF Viewer considers that the file argument is an attachment reference and fails to parse it. The second macro call renders properly, even though it's also an external URL.

[trrenty]

Hello @aubincleme , this attachment URL http://dev.xwiki.org/xwiki/bin/download/GoogleSummerOfCode/gsoc.pdf is not valid because it points to a terminal page without a parent. The correct URL would be http://dev.xwiki.org/xwiki/bin/download/GoogleSummerOfCode/WebHome/gsoc.pdf (note the presence of WebHome).

I will close this issue as invalid. Feel free to reopen it if you can reproduce it with other URLs.