Fix Windows build.

Change-Id: I7a8c5f16ec4ee17ec491229c7c15f9571d763d5c
Reviewed-on: https://gerrit.libreoffice.org/69710
Tested-by: Jenkins
Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>

sfx2/source/appl/appdde.cxx

@@ -43,6 +43,7 @@
 #include <sfx2/sfxsids.hrc>
 #include <helper.hxx>
 #include <sfx2/docfile.hxx>
+#include <ucbhelper/content.hxx>
 #include <comphelper/processfactory.hxx>
 #include <com/sun/star/ucb/CommandAbortedException.hpp>
 #include <com/sun/star/ucb/IllegalIdentifierException.hpp>