Fix device filter being ignored (missing await on util.isEmpty)

[TekScene]

Fixes #283 — "Filter by device(s) no longer filtering".

Cause

utility.isEmpty() is declared async, so it always returns a Promise, which is always truthy. The guard added in 3f3bab9 calls it without await:

if(devices.length > 0 && !util.isEmpty(medCard.playerDevice) && ...) okToAdd = false;

!util.isEmpty(...) therefore evaluates to false for every session, so the whole condition short-circuits and okToAdd is never set to false by the device filter. Result: all devices are shown regardless of the "Filter by device(s)" setting — matching the reports that rolling back to v1.21.9 (before that commit) restores correct behaviour.

Quick demonstration of the underlying behaviour:

!isEmpty("Shield")           -> false   // Promise is truthy
!isEmpty("")                 -> false
!(await isEmpty("Shield"))   -> true    // correct

Fix

Await the call, matching how util.isEmpty is used everywhere else in plex.js (e.g. lines 274, 321, 736). This is the only unawaited call site in the codebase.

if(devices.length > 0 && !(await util.isEmpty(medCard.playerDevice)) && ...) okToAdd = false;

The surrounding code is already inside an async reduce callback, so await is valid here. The null-safety intent of the original commit is preserved: sessions with no Player.title still skip the device check instead of throwing on .toLowerCase().