Fix coredump: when stream context is null

[ZhiyangLeeCN]

Function md5_file internal call php_stream_open_wrapper macro open stream according to filename argument passed function, this macro use is null stream context and send to _php_stream_open_wrapper_ex , but function socket_enable_crypto in ext-src/swoole_runtime.cc not check stream context is null, when use https url send to functionmd5_file occur coredump.

[codecov]

Codecov Report

Merging #4016 (f2d886b) into master (b1a0dcc) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4016      +/-   ##
==========================================
- Coverage   49.35%   49.22%   -0.14%     
==========================================
  Files          69       69              
  Lines       13063    13063              
==========================================
- Hits         6447     6430      -17     
- Misses       6616     6633      +17     

Impacted Files	Coverage Δ
src/os/async_thread.cc	66.37% <0.00%> (-3.50%)	⬇️
src/core/channel.cc	70.87% <0.00%> (-0.98%)	⬇️
src/coroutine/socket.cc	41.95% <0.00%> (-0.54%)	⬇️
src/server/port.cc	53.74% <0.00%> (-0.33%)	⬇️
src/network/socket.cc	58.15% <0.00%> (-0.22%)	⬇️
src/network/client.cc	44.42% <0.00%> (-0.19%)	⬇️

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