Fix MissingMandatoryParametersException for share notifications

[nickvergessen]

The routing system is non-forgiving.

@rullzer @schiessle

Steps

1. Enable share notifications
2. Set up a second user with email
3. Share a file with the user
4. Send notification

Expected

Email is sent, return is 200

Actual

Symfony\Component\Routing\Exception\MissingMandatoryParametersException
Some mandatory parameters are missing ("fileid") to generate a URL for route "files.viewcontroller.showFile"

No email

Fix #1277

[mention-bot]

@nickvergessen, thanks for your PR! By analyzing the annotation information on this pull request, we identified @rullzer, @LukasReschke and @schiessle to be potential reviewers

[MorrisJobke]

Tested and works 👍

[rullzer]

LGTM