gh-135698: Fix Cross-interpreter Queue.full() With Negative/Default max_size (gh-135724)

We weren't handling non-positive maxsize values (including the default) properly
in Queue.full().  This change fixes that and adjusts an associated assert.

Modules/_interpqueuesmodule.c

@@ -707,8 +707,11 @@ _queue_is_full(_queue *queue, int *p_is_full)
         return err;
     }
 
-    assert(queue->items.count <= queue->items.maxsize);
-    *p_is_full = queue->items.count == queue->items.maxsize;
+    assert(queue->items.maxsize <= 0
+           || queue->items.count <= queue->items.maxsize);
+    *p_is_full = queue->items.maxsize > 0
+        ? queue->items.count == queue->items.maxsize
+        : 0;
 
     _queue_unlock(queue);
     return 0;