packaging-check-invariants: check if 'component' is in 'branch' before using it

Sometimes, we need to import and modify packages from Debian. To make the initial review easier, an apertis/v202* branch is created from the debian one, then a merge request is created against it adding debian/apertis/* files. During the review, the apertis branch doesn't have any debian/apertis/* files and the dashboard fails with:

  Traceback (most recent call last):
    File "/builds/infrastructure/dashboard/./bin/packaging-check-invariants", line 857, in <module>
      checker.check_git_and_obs_versions(package)
    File "/builds/infrastructure/dashboard/./bin/packaging-check-invariants", line 271, in check_git_and_obs_versions
      component = branch.component
                ^^^^^^^^^^^^^^^^
    File "/builds/infrastructure/dashboard/./bin/packaging-check-invariants", line 79, in __getattr__
      item = super(DictWrapper, self).__getitem__(attr)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  KeyError: 'component'
  The above exception was the direct cause of the following exception:
  Traceback (most recent call last):
    File "/builds/infrastructure/dashboard/./bin/packaging-check-invariants", line 867, in <module>
      raise Error(package.name) from e

See: pkg/opencv!2 (comment 129850)

Signed-off-by: Dylan Aïssi dylan.aissi@collabora.com