Prevent null argument from crashing ClockEventController

Kotlin appears to zealously check whether the timeFormat argument
is null to protect us from NPEs, even though it is not used. In an
edge where a null value is passed, this causes a crash.

Test: N/A
Bug: 267477766
Change-Id: Ie302018c8ab142d26ab8ffd18e2157cdcd1602da

packages/SystemUI/src/com/android/keyguard/ClockEventController.kt

@@ -259,7 +259,7 @@ constructor(
                 largeTimeListener?.update(shouldTimeListenerRun)
             }
 
-            override fun onTimeFormatChanged(timeFormat: String) {
+            override fun onTimeFormatChanged(timeFormat: String?) {
                 clock?.events?.onTimeFormatChanged(DateFormat.is24HourFormat(context))
             }