tdf#125846 - Avoid deleting fly formats one by one

Avoid deleting fly formats one by one while the document is destroyed
since DeleteAndDestroyAll removes all fly formats at once in
SwDoc::~SwDoc afterwards.

Change-Id: Ie62ead75a3ba1cdfa47d072c329e8d9fec9387ac
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/211864
Reviewed-by: Andreas Heinisch <andreas.heinisch@yahoo.de>
Tested-by: Jenkins

sw/source/core/txtnode/thints.cxx

@@ -1259,7 +1259,8 @@ void SwTextNode::DestroyAttr( SwTextAttr* pAttr )
     case RES_TXTATR_FLYCNT:
         {
             SwFrameFormat* pFormat = pAttr->GetFlyCnt().GetFrameFormat();
-            if( pFormat )      // set to 0 by Undo?
+            // tdf#125846 - avoid deleting fly formats one by one while the document is destroyed
+            if (pFormat && !rDoc.IsInDtor()) // set to 0 by Undo?
                 rDoc.getIDocumentLayoutAccess().DelLayoutFormat( pFormat );
         }
         break;