Mark destroyed resources as unused.

* This prevents bogus double free errors if reshListDestruct encounters
  an error that triggers itself again via at_exit.

src/resource_handle.c

@@ -178,6 +178,7 @@ reshListDestruct(int namespaceID)
           listElem_t *listElem = resHList[namespaceID].resources + j;
           if (listElem->status & RESH_IN_USE_BIT)
             listElem->res.v.ops->valDestroy(listElem->res.v.val);
+          listElem->status = RESH_UNUSED;
         }
       Free(resHList[namespaceID].resources);
       resHList[namespaceID].resources = NULL;