Avoid unnecessary bad downcasts to SwCharFmt

At least in JunitTest_sw_unoapi it happens that this downcast is called from
~SwCharFmt -> ~SwFmt -> SwClient::ModifyNotification -> SwDepend::Modify ->
SwClient::ModifyNotification -> SwEndNodeInfo::Modify, i.e., the downcasted
object is in destruction and no longer an SwCharFmt but only an SwFmt.  Whether
or not that chain of calls is actually sane---casting down to merely an SwFmt
is a quickfix at least.

Change-Id: I33f0d76c42daa2530b8d417df059de57190c5070

sw/source/core/doc/docftn.cxx

@@ -193,9 +193,9 @@ void SwEndNoteInfo::Modify( const SfxPoolItem* pOld, const SfxPoolItem* pNew )
     {
         SwDoc* pDoc;
         if( aCharFmtDep.GetRegisteredIn() )
-            pDoc = static_cast<SwCharFmt*>(aCharFmtDep.GetRegisteredIn())->GetDoc();
+            pDoc = static_cast<SwFmt*>(aCharFmtDep.GetRegisteredIn())->GetDoc();
         else
-            pDoc = static_cast<SwCharFmt*>(aAnchorCharFmtDep.GetRegisteredIn())->GetDoc();
+            pDoc = static_cast<SwFmt*>(aAnchorCharFmtDep.GetRegisteredIn())->GetDoc();
         SwFtnIdxs& rFtnIdxs = pDoc->GetFtnIdxs();
         for( size_t nPos = 0; nPos < rFtnIdxs.size(); ++nPos )
         {