tdf#123067: fix assert when exporting template

See bt here:
https://bugs.documentfoundation.org/attachment.cgi?id=148772

Change-Id: I7bd6a7dcb7cf7677b92abe79abb781105dfb6019
Reviewed-on: https://gerrit.libreoffice.org/67285
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

ucb/source/ucp/file/filtask.cxx

@@ -1418,7 +1418,7 @@ TaskManager::copy(
         }
         case NameClash::RENAME:
         {
-            OUString newDstUnqPath;
+            OUString newDstUnqPath = dstUnqPath;
             nError = copy_recursive( rslvdSrcUnqPath,dstUnqPath,IsWhat,true );
 
             if( nError == osl::FileBase::E_EXIST )