Fix: Extension crashing, when no associatedRole can be found

There are situations, where no `associatedRole` for a given
`indicatorContainer` can be found (e.g. the GameMode GNOME Shell
Extension seems to cause such a situation, when you have it enabled and
lock and unlock GNOME).
Previously this would crash the extension. With this fix, those
`indicatorContainer`s just get ignored.

src/extension.js

@@ -353,6 +353,7 @@ class Extension {
                 // First get the role associated with the current indicator
                 // container.
                 const associatedRole = indicatorContainerRoleMap.get(indicatorContainer);
+                if (!associatedRole) continue;
 
                 // Handle an AppIndicator/KStatusNotifierItem item differently.
                 if (associatedRole.startsWith("appindicator-")) {