usb: Fixed the null pointer issue

Bug: 200323450
Test: Function work with reboot connect to PC and HU

Signed-off-by: Ricky Niu <rickyniu@google.com>
Change-Id: I9bdfcda195c30d71d9d39e1170bbf66a7021c39b

services/usb/java/com/android/server/usb/UsbDeviceManager.java

@@ -237,7 +237,12 @@ public class UsbDeviceManager implements ActivityTaskManagerInternal.ScreenObser
         @Override
         public void onUEvent(UEventObserver.UEvent event) {
             if (DEBUG) Slog.v(TAG, "USB UEVENT: " + event.toString());
-            sEventLogger.log(new UsbDeviceLogger.StringEvent("USB UEVENT: " + event.toString()));
+            if (sEventLogger != null) {
+                sEventLogger.log(new UsbDeviceLogger.StringEvent("USB UEVENT: "
+                        + event.toString()));
+            } else {
+                if (DEBUG) Slog.d(TAG, "sEventLogger == null");
+            }
 
             String state = event.get("USB_STATE");
             String accessory = event.get("ACCESSORY");