Fix failure to set unlimited_access property on non-existent pool.

[dbernstein]

Description

Simply checks if the pool is not None before trying to set a property on it.
Improves logging to show detailed failure info in logs during OPDS feed imports so that future issues will be easier to troubleshoot in the future.

One thing I'm not sure about: does it make sense for the pool to be returned as a None from super().update_work_for_e dition

Motivation and Context

https://ebce-lyrasis.atlassian.net/browse/PP-192

How Has This Been Tested?

I reran San Rafael BiblioBoard collection locally and confirmed that all 139 failures are no longer occurring.

./bin/opds_for_distributors_import_monitor --collection "San Rafael BiblioBoard" --force
...
99d7-25f0535356c6: rel=alternate", "timestamp": "2023-09-22T17:57:25.570186+00:00"}
{"host": "8e97e3d1a6b0", "app": "simplified", "name": "OPDS for Distributors Import Monitor", "level": "INFO", "filename": "monitor.py", "message": "[San Rafael BiblioBoard] Items imported: 30379. Failures: 0.", "timestamp": "2023-09-22T17:57:25.652138+00:00"}
{"host": "8e97e3d1a6b0", "app": "simplified", "name": "OPDS for Distributors Import Monitor", "level": "INFO", "filename": "monitor.py", "message": "[San Rafael BiblioBoard] Ran OPDS for Distributors Import Monitor monitor in 3664.29 sec.", "timestamp": "2023-09-22T17:57:25.657573+00:00"}

Checklist

• [/] I have updated the documentation accordingly.
• [] All new and existing tests passed.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ac78b47) 90.17% compared to head (540b347) 90.17%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1402   +/-   ##
=======================================
  Coverage   90.17%   90.17%           
=======================================
  Files         226      226           
  Lines       29871    29872    +1     
  Branches     6845     6845           
=======================================
+ Hits        26936    26938    +2     
+ Misses       1893     1892    -1     
  Partials     1042     1042           

Files Changed	Coverage Δ
core/opds_import.py	89.18% <100.00%> (+0.01%)	⬆️

... and 1 file with indirect coverage changes

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[dbernstein]

One thing I'm not sure about: does it make sense for the pool to be returned as a None from super().update_work_for_edition. The update_work_for_edition seems to allow for it and downstream code seems to expect it, but I'm wondering if makes sense in this context.

[jonathangreen]

It does seem like the super class expects to return None in some cases. So I think this is an okay fix.

[jonathangreen]

Looks good to me.