Merge pull request #4695 from wfwzhxd/wfwzhxd-patch-1

注释错误，此处的场景是zone满了，不是空了

src/slab.c

@@ -540,7 +540,7 @@ void *rt_malloc(rt_size_t size)
     {
         RT_ASSERT(z->z_nfree > 0);
 
-        /* Remove us from the zone_array[] when we become empty */
+        /* Remove us from the zone_array[] when we become full */
         if (--z->z_nfree == 0)
         {
             zone_array[zi] = z->z_next;