[Merge] ~azzar1/unity:fix-1733557 into unity:master

[Andrea Azzarone]

The proposal to merge ~azzar1/unity:fix-1733557 into unity:master has been updated.

Commit message changed to:

locksreen: cancel authentication if externally unlocked

The lockscreen can be externellay unlocked. This happens e.g. when
you unlock the session from LightDM or from the CLI. We need to
cancel the authentication in order to ensure that the next one does
not fail.

Fixes: https://bugs.launchpad.net/unity/+bug/1733557

For more details, see:
https://code.launchpad.net/~azzar1/unity/+git/unity/+merge/363124
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Your team Unity Team is requested to review the proposed merge of ~azzar1/unity:fix-1733557 into unity:master.