Fixing labels manager interface

[fercer]

Fixes incorrect disabling/enabling of navigation buttons on the labels manager widget.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 10.00000% with 45 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@8fe4008). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/napari_activelearning/_labels.py	10.25%	35 Missing ⚠️
src/napari_activelearning/_interface.py	0.00%	7 Missing ⚠️
src/napari_activelearning/_layers.py	25.00%	3 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #14   +/-   ##
=======================================
  Coverage        ?   70.20%           
=======================================
  Files           ?       13           
  Lines           ?     3397           
  Branches        ?        0           
=======================================
  Hits            ?     2385           
  Misses          ?     1012           
  Partials        ?        0           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.