fix dead lock while get connecions

[qzhuyan]

Catched by proper tests,

In quicer:get_connections call, while holding the lock of r_ctx, deref c_ctx may cause connection close and then trigger callback that destroy c_ctx which try to lock r_ctx in another thread, causing dead lock.

solution is to deref c_ctx after unlock r_ctx.

[coveralls]

Pull Request Test Coverage Report for Build 8171327323

Details

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 87.361%

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Files with Coverage Reduction	New Missed Lines	%
src/quicer_stream.erl	1	78.72%

Totals
Change from base Build 8094481333:	0.2%
Covered Lines:	3774
Relevant Lines:	4320

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💛 - Coveralls