回调被多次调用。
回调几乎总是意味着只被调用一次，因为查询可以被履行或被拒绝，但不能同时被执行。
后者可以通过多次调用回调来实现。
A callback was called more than once.
A callback is almost always meant to only be called once as the query
can either be fulfilled or rejected but not both at the same time. The latter
would be possible by calling a callback more than once.