Add null check to KeyEventDispatcher.

Make sure we don't try to dispatch key events to services
that have died. Doing so crashes the device.

Bug: 30866905
Change-Id: I1cc0515cca8924b0c2744de98ac75a901b94246d

services/accessibility/java/com/android/server/accessibility/KeyEventDispatcher.java

@@ -121,7 +121,7 @@ public class KeyEventDispatcher {
             Service service = boundServices.get(i);
             // Key events are handled only by services that declared
             // this capability and requested to filter key events.
-            if (!service.mRequestFilterKeyEvents) {
+            if (!service.mRequestFilterKeyEvents || (service.mServiceInterface == null)) {
                 continue;
             }
             int filterKeyEventBit = service.mAccessibilityServiceInfo.getCapabilities()