tdf#122722 sw: fix hidden text crash in SwTextFrame::GetCurWord()

A frame that is fully hidden does not have a SwParaPortion,
see SwTextFrame::Format() early return.

(regression from 9bda4a67)

Change-Id: I6b06824e53cef7218b60f60fced8f863adad8b62
Reviewed-on: https://gerrit.libreoffice.org/66385
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>

sw/source/core/txtnode/txtedt.cxx

@@ -703,7 +703,7 @@ OUString SwTextFrame::GetCurWord(SwPosition const& rPos) const
     OUString const& rText(GetText());
     assert(sal_Int32(nPos) <= rText.getLength()); // invalid index
 
-    if (rText.isEmpty())
+    if (rText.isEmpty() || IsHiddenNow())
         return OUString();
 
     assert(g_pBreakIt && g_pBreakIt->GetBreakIter().is());