Do not fail when uniqueId field is missing

On some devices, DisplayInfo does not have a "uniqueId" field. This
field is only used for correct UHID behavior on virtual displays, so its
absence should not prevent scrcpy from working.

Refs #6009 <https://github.com/Genymobile/scrcpy/pull/6009>
Fixes #6461 <https://github.com/Genymobile/scrcpy/issues/6461>