Don't raise keyerror during migration, if missing camera key

[prairiesnpr]

Resolves #494

If user has never configured the camera, the ENABLE_CAMERA key is missing.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (3d8be13) 98.93% compared to head (1d629f6) 98.93%.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #495   +/-   ##
=======================================
  Coverage   98.93%   98.93%           
=======================================
  Files          16       16           
  Lines        1315     1315           
=======================================
  Hits         1301     1301           
  Misses         14       14           

Impacted Files	Coverage Δ
custom_components/husqvarna_automower/__init__.py	100.00% <100.00%> (ø)
...stom_components/husqvarna_automower/config_flow.py	93.91% <100.00%> (ø)

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[robinostlund]

Can verify that this solved my issues 👍