tdf#116555 filter: make sure default extension for HTML is not .xhtml

Since by default we don't write XHTML markup in the sw HTML export.

Change-Id: Ifbf9850652d7838582725be391b2fd1a062495e5
Reviewed-on: https://gerrit.libreoffice.org/52663Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

filter/source/config/fragments/types/generic_HTML.xcu

@@ -18,7 +18,8 @@
     <node oor:name="generic_HTML" oor:op="replace" >
         <prop oor:name="DetectService"><value>com.sun.star.comp.filters.PlainTextFilterDetect</value></prop>
         <prop oor:name="URLPattern"><value>private:factory/swriter/web*</value></prop>
-        <prop oor:name="Extensions"><value>html htm xhtml</value></prop>
+        <!-- the last extension is used when the code wants to know the extension of this type -->
+        <prop oor:name="Extensions"><value>html xhtml htm</value></prop>
         <prop oor:name="MediaType"><value>text/html</value></prop>
         <prop oor:name="Preferred"><value>false</value></prop>
         <prop oor:name="PreferredFilter"><value>HTML</value></prop>