fix: filter out contacts with empty email addresses in sharee completion

[juliusknorr]

Otherwise contacts without an email address would still show up when sharing or adding them to a circle, which is not possible as there is no destination to share to

[juliusknorr]

Using filter_var now as per feedback from @blizzz

[juliusknorr]

/backport! to stable31

[juliusknorr]

/backport! to stable30

[juliusknorr]

/backport! to stable29

[Pytal]

/backport! to stable29

[backportbot]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/51707/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 87e12884

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/51707/stable29

Error: Failed to create pull request: Validation Failed: {"resource":"PullRequest","code":"custom","message":"A pull request already exists for nextcloud:backport/51707/stable29."} - https://docs.github.com/rest/pulls/pulls#create-a-pull-request

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.