Small correction in 'traverseweakvalue'

After a weak table is traversed in the atomic phase, if it does not
have white values ('hasclears') it does not need to be retraversed
again. (Comments were correct, but code did not agree with them.)

lgc.c

@@ -497,10 +497,10 @@ static void traverseweakvalue (global_State *g, Table *h) {
         hasclears = 1;  /* table will have to be cleared */
     }
   }
-  if (g->gcstate == GCSatomic && hasclears)
-    linkgclist(h, g->weak);  /* has to be cleared later */
-  else
+  if (g->gcstate == GCSpropagate)
     linkgclist(h, g->grayagain);  /* must retraverse it in atomic phase */
+  else if (hasclears)
+      linkgclist(h, g->weak);  /* has to be cleared later */
 }