[4.6] Fix crash when discovery fails while using -p no:terminal

[asottile]

via #5506

[codecov]

Codecov Report

Merging #5508 into 4.6-maintenance will decrease coverage by 56.76%.
The diff coverage is 40%.

@@                 Coverage Diff                  @@
##           4.6-maintenance    #5508       +/-   ##
====================================================
- Coverage            95.92%   39.15%   -56.77%     
====================================================
  Files                  115      115               
  Lines                26433    26437        +4     
  Branches              2610     2472      -138     
====================================================
- Hits                 25355    10352    -15003     
- Misses                 755    15430    +14675     
- Partials               323      655      +332

Impacted Files	Coverage Δ
src/_pytest/nodes.py	74.5% <100%> (-20.1%)	⬇️
testing/test_config.py	15.61% <25%> (-83.89%)	⬇️
testing/test_reports.py	10.49% <0%> (-89.51%)	⬇️
testing/logging/test_reporting.py	12.21% <0%> (-87.46%)	⬇️
testing/code/test_excinfo.py	11.63% <0%> (-85.13%)	⬇️
testing/test_collection.py	15.06% <0%> (-84.75%)	⬇️
testing/test_cacheprovider.py	15.36% <0%> (-84.39%)	⬇️
testing/test_junitxml.py	14.06% <0%> (-83.91%)	⬇️
testing/test_pluginmanager.py	16.52% <0%> (-83.48%)	⬇️
... and 95 more

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