files: fix exception when share-attributes is undefined

[pulsejet]

Fixes crash when calling Sidebar::open() from Memories.

EDIT: It's been a while I can't remember the process .. should I compile the JS in the first commit or with the bot?

[artonge]

EDIT: It's been a while I can't remember the process .. should I compile the JS in the first commit or with the bot?

Both are ok :).

[pulsejet]

/compile amend /

[skjnldsv]

/backport to stable31

[skjnldsv]

/backport to stable30

[skjnldsv]

/backport to stable29

[skjnldsv]

Not needed for older branches

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