Fix some warnings#36

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mingkuang-Chuyu wants to merge 2 commits intocoderforlife:masterfrom

mingkuang-Chuyu:master

Commits on Aug 5, 2020

fix CircularBuffer operator=, No explicit return value.
mingkuang-Chuyu
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fix SET_ERROR, INIT_STREAM_ERROR_MESSAGE, SET_WARNING, INIT_STREAM_WARNING_MESSAGE maybe Null pointer used.
mingkuang-Chuyu
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