sw: remove bogus assert in SwDoc::IsInHeaderFooter()

If the for loop has a break after the first frame anchored on that node,
it makes no sense to assert that all frames have been visited.

(regression from bb95f7e6)

Change-Id: Ibd8d65f286b441127be7735c63f4b84ba94dcb6f

sw/source/core/doc/doclay.cxx

@@ -1553,9 +1553,6 @@ bool SwDoc::IsInHeaderFooter( const SwNodeIndex& rIdx ) const
             OSL_ENSURE(mbInReading, "Found a FlySection but not a Format!");
             return false;
         }
-#if OSL_DEBUG_LEVEL > 0
-        assert( checkFmts.empty());
-#endif
     }
 
     return 0 != pNd->FindHeaderStartNode() ||