🐛 Fix regression in scanner for root-level series

[aaronleopold]

A cherry-pick of 61e7dbd which contains a fix for root-level series scanning (i.e. the library itself is a series)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
core/src/filesystem/scanner/series_scan_job.rs	0.00%	14 Missing ⚠️
core/src/filesystem/scanner/walk.rs	0.00%	7 Missing ⚠️
core/src/filesystem/scanner/library_scan_job.rs	0.00%	3 Missing ⚠️

Files with missing lines	Coverage Δ
core/src/db/entity/library/entity.rs	2.54% <ø> (ø)
core/src/filesystem/scanner/library_scan_job.rs	0.00% <0.00%> (ø)
core/src/filesystem/scanner/walk.rs	0.00% <0.00%> (ø)
core/src/filesystem/scanner/series_scan_job.rs	0.00% <0.00%> (ø)