coverity#1267639: logically dead code in SwUndo::UndoWithContext()

Change-Id: I5e41337705bb2952a98e7e5778a217cfb2caccdb

sw/source/core/undo/undobj.cxx

@@ -210,7 +210,6 @@ void SwUndo::UndoWithContext(SfxUndoContext & rContext)
     ::sw::UndoRedoContext *const pContext(
             dynamic_cast< ::sw::UndoRedoContext * >(& rContext));
     assert(pContext);
-    if (!pContext) { return; }
     const UndoRedoRedlineGuard aUndoRedoRedlineGuard(*pContext, *this);
     UndoImpl(*pContext);
 }