Don't override the default port if a value of 0 is sent explicitly

[macabu]

Some encoders like the Cerevo LiveShell 2 will send explicitly port 0 if you don't set any port. While it should default to not send any actual port or default the protocol's default (1935 for RTMP etc), it doesn't do that unfortunately.

[2020-05-11 13:28:40.286][Error][1][5645][11] serve error code=2006 : service cycle : rtmp: stream service : discovery tcUrl failed, tcUrl=rtmp://localhost:0/live, schema=rtmp, vhost=__defaultVhost__, port=0, app=live
thread [1][5645]: do_cycle() [src/app/srs_app_rtmp_conn.cpp:210][errno=11]
thread [1][5645]: service_cycle() [src/app/srs_app_rtmp_conn.cpp:399][errno=11]
thread [1][5645]: stream_service_cycle() [src/app/srs_app_rtmp_conn.cpp:457][errno=11](Resource temporarily unavailable)

This small patch makes it so that if a port 0 is sent, the default value of port will not be overridden.

[codecov-commenter]

Codecov Report

Merging #1754 into develop will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #1754      +/-   ##
===========================================
+ Coverage    58.13%   58.16%   +0.03%     
===========================================
  Files          116      116              
  Lines        48306    48286      -20     
===========================================
+ Hits         28082    28086       +4     
+ Misses       20224    20200      -24     

| Impacted Files | Coverage Δ | |'

'| Impacted Files | Coverage Δ | |
|---|---|---|
| trunk/src/kernel/srs_kernel_utility.cpp | 93.38% <100.00%> (ø) | |
| trunk/src/utest/srs_utest_kernel.cpp | 98.43% <100.00%> (+<0.01%) | ⬆️ |
| trunk/src/core/srs_core_autofree.hpp | 88.88% <0.00%> (-11.12%) | ⬇️ |
| trunk/src/app/srs_app_gb28181.hpp | 0.00% <0.00%> (ø) | |
| trunk/src/app/srs_app_rtc_sdp.hpp | 0.00% <0.00%> (ø) | |

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0b9887b...5633af0. Read the comment docs.

TRANS_BY_GPT3

[winlinvip]

👍

I will merge this to SRS 4.0.

Very nice PR with utest.