What is the purpose of the change

Fixed a bug described in Dubbo-1765

If the provider is temporarily unavailable, the reference bean initialization will failed with exception. However, the initialized flag will be set to true, which will cause spring to hold a NULL_OBJECT cache. The subsequent call will always get a null instance.

This change will allow the consumer to obtain the correct instance when provider become available.

Brief changelog

• Set initialized=false in ReferenceConfig when provider is not available.

Verifying this change

unit test passed

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