tdf#90333 Dictionaries Path Cannot Be Changed

PathSettings::impl_storePath wants to be able to nil the Dictionaries
path in the old copy of properties

Change-Id: Id579914cfa8b459efce962d304e2f9d6185bd55f
Reviewed-on: https://gerrit.libreoffice.org/64115
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

officecfg/registry/schema/org/openoffice/Office/Common.xcs

@@ -1616,7 +1616,7 @@
           </info>
           <value>$(insturl)/@LIBO_SHARE_FOLDER@/config</value>
         </prop>
-        <prop oor:name="Dictionary" oor:type="xs:string" oor:nillable="false">
+        <prop oor:name="Dictionary" oor:type="xs:string">
           <info>
             <desc>Contains the provided dictionaries.</desc>
           </info>