tdf#102073: sw: do not create SwFootnoteNumPortion inside table

The SwTextFormatter::WhichFirstPortion() wants to create a new
SwFootnoteNumPortion for the first paragraph in every cell, because it
doesn't have mpPrev set and SwTextFrame::IsFootnoteNumFrame() is true,
and somehow this even causes an infinite loop in the bugdoc because
initially nothing more than the footnote number fits inside a line.

Just detect that it's inside a table and return false then.

Change-Id: I1f010f1242d53d9f99a4d3a4f6fc3cee65aa3958

sw/source/core/text/txtftn.cxx

@@ -57,6 +57,8 @@ using namespace ::com::sun::star;
 
 bool SwTextFrame::IsFootnoteNumFrame_() const
 {
+    if (IsInTab())
+        return false; // tdf#102073 first frame in cell doesn't have mpPrev set
     const SwFootnoteFrame* pFootnote = FindFootnoteFrame()->GetMaster();
     while( pFootnote && !pFootnote->ContainsContent() )
         pFootnote = pFootnote->GetMaster();