title: Frontend-editing broken when text contains internal links
body: <p>We are using TYPO3 8.7.19 with the extension frontend_editing (Version: 1.4.0) and CoolURI. We still use css_styled_content.</p>
  
  <p>When editing a content element in the frontend with the „frontent-editing bar”, e.g. text I get an error, but only, if it contains an internal link.
  The changes are not saved. It crash with:</p>
  
  <pre><code>Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1460629247: No valid handlers found for type: unknown | TYPO3\CMS\Core\LinkHandling\Exception\UnknownLinkHandlerException thrown in file /usr/share/typo3/typo3_src-8.7.19/typo3/sysext/core/Classes/LinkHandling/LinkService.php in line 163. Requested URL: https://www.mysite.de/typo3/index.php?ajaxID=%2Fajax%2Ffrontend-editing%2Fprocess&amp;ajaxToken=--AnonymizedToken--&amp;page=123
  </code></pre>
  
  <p>There is a <a href="https://github.com/FriendsOfTYPO3/frontend_editing/issues/305" rel="nofollow noreferrer">bug report</a>  and a suggested <a href="https://github.com/FriendsOfTYPO3/frontend_editing/issues/305#issuecomment-428728766" rel="nofollow noreferrer">solution</a> für TYPO3 9.5.x and a <a href="https://bitbucket.org/snippets/scw_bihlmaier/5ezpaB" rel="nofollow noreferrer">solution</a> for TYPO3 8.7.x</p>
  
  <p>Unfortunately, I don't know how to realize that solution for my system, cause</p>
  
  <ol>
  <li>wee use coolURI but not the required realurl-xtension.</li>
  <li>I don't know where to add the suggested code</li>
  </ol>
  
  <p>Any hints for me?</p>