RTC: fix play rtc judge for rtmp inactive.(#2863)

[chundonglinlin]

After the RTMP publishing is disconnected, then I publish RTC stream and the RTC playing will be rejected.Likely:
My config as follows,

vhost __defaultVhost__ {
    rtc {
        enabled     on;
        # @see https://github.com/ossrs/srs/wiki/v4_CN_WebRTC#rtmp-to-rtc
        rtmp_to_rtc off;
        # @see https://github.com/ossrs/srs/wiki/v4_CN_WebRTC#rtc-to-rtmp
        rtc_to_rtmp off;
    }
}

Firstly, publish rtmp stream, then disconnect.
ffmpeg -re -i 264_aac.flv -c copy -f flv rtmp://127.0.0.1/live/livestream
Secondly, publish rtc stream.
./objs/srs_bench -pr webrtc://localhost/live/livestream -sa avatar.ogg -sv avatar.h264 -fps 25
Thirdly, play is rejected.
./objs/srs_bench -sr webrtc://localhost/live/livestream

[codecov-commenter]

Codecov Report

Merging #2867 (27976ef) into 4.0release (2bc5e9a) will not change coverage.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           4.0release    #2867   +/-   ##
===========================================
  Coverage       60.22%   60.22%           
===========================================
  Files             121      121           
  Lines           51070    51070           
===========================================
  Hits            30756    30756           
  Misses          20314    20314           

| Impacted Files | Coverage Δ | |'

Translated to English while maintaining the markdown structure:

'| Impacted Files | Coverage Δ | |
|---|---|---|
| trunk/src/app/srs_app_rtc_api.cpp | 0.00% <0.00%> (ø) | |

Translated to English while maintaining the markdown structure:

| trunk/src/app/srs_app_rtc_api.cpp | 0.00% <0.00%> (ø) | |

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| Δ = absolute <relative> (impact), ø = not affected, ? = missing data |

Translated to English while maintaining the markdown structure:

| Δ = absolute <relative> (impact), ø = not affected, ? = missing data |

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