tdf#35798: use separate paragraphs for Label elements

Since commit db04be037b, empty Database
fields are hidden. But since Labels wizard generates a single paragraph
with line breaks for the label's text, the hiding feature cannot be
used efficiently.

Let the individual lines be in individual paragraphs.

Change-Id: I27430d54baea88461c2ea9de38baa95d6b7e9e62
Reviewed-on: https://gerrit.libreoffice.org/54800
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

sw/source/uibase/app/appenv.cxx

@@ -123,7 +123,7 @@ OUString InsertLabEnvText( SwWrtShell& rSh, SwFieldMgr& rFieldMgr, const OUStrin
             if ( !bField )
                 rSh.Insert( sTmpText );
         }
-        rSh.InsertLineBreak();
+        rSh.SplitNode();
     }
     rSh.DelLeft();  // Again remove last linebreak