Refuse edge request when state is stopping

[duiniuluantanqin]

Question: Edge: After the last pull stream is disconnected, if the same stream is requested again within 3 seconds, it cannot be played smoothly. (#2215)
Analysis: When the stream is requested again within 3 seconds, the state is in the stopping state.
Solution: When in the stopping state, return an error and provide the user with a clear prompt.

TODO: @IAmCodingCoding has provided an optimized solution that allows for quick exit without waiting for 3 seconds. See #2215 (comment).

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TRANS_BY_GPT3

[codecov-commenter]

Codecov Report

Merging #2707 (79b0929) into develop (0d8b2df) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #2707      +/-   ##
===========================================
- Coverage    59.98%   59.98%   -0.01%     
===========================================
  Files          121      121              
  Lines        51046    51048       +2     
===========================================
  Hits         30619    30619              
- Misses       20427    20429       +2     

| Impacted Files | Coverage Δ | |'

Translated to English while maintaining the markdown structure:

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

'

Translated to English while maintaining the markdown structure:

'| trunk/src/app/srs_app_edge.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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TRANS_BY_GPT3

[xiaozhihong]

st_sleep 3 seconds is to prevent excessive retries, so the current best practice is to provide clear instructions.

TRANS_BY_GPT3

[winlinvip]

NICE @duiniuluantanqin @xiaozhihong