Fix NPE when store brightness and displayDevice is null

This issue can cause a phone reboot, we have to make sure displayDevice is not null before getting its unique id.

Bug: 249782095
Test: manual
Change-Id: Iec57f44798820ac741bd2e6843874fb2b1aaef12

services/core/java/com/android/server/display/PersistentDataStore.java

@@ -300,8 +300,11 @@ final class PersistentDataStore {
     }
 
     public boolean setBrightness(DisplayDevice displayDevice, float brightness) {
+        if (displayDevice == null || !displayDevice.hasStableUniqueId()) {
+            return false;
+        }
         final String displayDeviceUniqueId = displayDevice.getUniqueId();
-        if (!displayDevice.hasStableUniqueId() || displayDeviceUniqueId == null) {
+        if (displayDeviceUniqueId == null) {
             return false;
         }
         final DisplayState state = getDisplayState(displayDeviceUniqueId, true);