Web content with relative link and anchor cannot be saved due to a "The content references a missing page" error

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X EE, Master
• Fix Version/s: 7.0.0 DXP FP24, 7.0.X EE, 7.0.4 CE GA5, 7.1.X, Master
• Component/s: Staging > Export/Import
• Labels:
  • liferay-digital-enterprise-70-sp5
  • liferay-fixpack-de-24-7010
• Branch Version/s:
  7.0.x
• Backported to Branch:
  Committed
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/49700

Description
If you try to publish a web content that contains a relative link and an anchor, the content cannot be saved due to a "The content references a missing page" error.

Steps to reproduce
1. Create a Web Content in the default Guest Site.
2. Edit the source for the content and copy in this html.

<p id="section1">Section 1</p>
<p id="section2">Section 2</p>
<p><a href="/web/guest/home#section2">Section 2</a><a href="#section2">Section 2 (anchor only)</a></p>

3. Click Save

Expected Result: The web content saves
Actual Result: The web content does not save and displays the error "The content references a missing page."

Reproduced in master (37cc85673fd99d837563e367f91ca81e7c470e9a)
Reproduced in ee-7.0.x (3d74b73e65685db9f0090608ccc07f454d026afe)