Fix assert statement

which I messed up in 7e4db91a
  "Convert SfxShellStack_Impl from SfxPtrArr to std::vector"

Change-Id: I177972fddb8a0f2237085fdc2892d6992c5fc746

sfx2/source/control/dispatch.cxx

@@ -1588,7 +1588,7 @@ void SfxDispatcher::FlushImpl()
         if(i->bPush)
         {
             // Actually push
-            DBG_ASSERT( std::find(pImp->aStack.begin(), pImp->aStack.end(), i->pCluster) != pImp->aStack.end(),
+            DBG_ASSERT( std::find(pImp->aStack.begin(), pImp->aStack.end(), i->pCluster) == pImp->aStack.end(),
                        "pushed SfxShell already on stack" );
             pImp->aStack.push_back(i->pCluster);
             i->pCluster->SetDisableFlags(pImp->nDisableFlags);