Remove the session from the pool if the selection failed

[leszko]

Related to this Discord thread.

Problem:

• The Orch session is stored as inUse
• But the Orch is busy
• Then, we keep on retrying it instead of making the discovery again

Solution:
If the selection failed, then remove the session from the pool (it will anyway be added in the next 6 min, because we make discovery process every 6 min).

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 31.92328%. Comparing base (fdebf7f) to head (41150dc).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
server/ai_process.go	0.00000%	4 Missing ⚠️
server/ai_session.go	0.00000%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3695         +/-   ##
===================================================
- Coverage   31.93229%   31.92328%   -0.00901%     
===================================================
  Files            156         156                 
  Lines          47441       47445          +4     
===================================================
- Hits           15149       15146          -3     
- Misses         31398       31404          +6     
- Partials         894         895          +1     

Files with missing lines	Coverage Δ
server/ai_session.go	7.20930% <0.00000%> (ø)
server/ai_process.go	1.67504% <0.00000%> (-0.00563%)	⬇️

... and 2 files with indirect coverage changes

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Files with missing lines	Coverage Δ
server/ai_session.go	7.20930% <0.00000%> (ø)
server/ai_process.go	1.67504% <0.00000%> (-0.00563%)	⬇️

... and 2 files with indirect coverage changes

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