Add Signature dialog fails if no signatures in database

[Fubble J. Skag]

Ran into this on private after resetting database and assumed it was a one-off but another user reported the same in Discord after a fresh install. Issue goes away if/when signatures are pasted.

Corresponds with a JS error in console:

‌

Uncaught TypeError: Cannot read properties of null (reading 'undefined')
    at HTMLElement.openSignatureDialog (signature-dialog.js:34)
    at HTMLElement.dispatch (jquery-3.3.1.min.js:2)
    at HTMLElement.y.handle (jquery-3.3.1.min.js:2)

‌

[Astriania]

Upgrading as this will likely affect every new self-hosted instance

[Fubble J. Skag]

This was fixed in PR 188