fix TLS infinite loop when peer close the connection unexpectedly

[Guest0x0]

OpenSSL's SSL_read/SSL_write does not seem to handle zero return from the underlying BIO correctly. It keeps reporting SSL_WANT_READ in this case, instead of SSL_ZERO_RETURN or others. So if the peer closed the underlying connection unexpectedly when @tls.Tls is attempting a read (e.g. in connect or read), current implementation falls into infinite loop. This PR fixes the issue and handle peer connection close properly.

[coveralls]

Pull Request Test Coverage Report for Build 713

Details

• 1 of 2 (50.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 78.011%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/tls/tls.mbt	1	2	50.0%

Totals
Change from base Build 712:	0.09%
Covered Lines:	1224
Relevant Lines:	1569

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💛 - Coveralls