Fix DREAMING_STARTED broadcast.

This change fixes a bug where DREAMING_STARTED intent is only broadcast
once because mSentStartBroadcast flag is not being reset after
DREAM_STOPPED intent is broadcast.

Bug: 255732899
Fix: 255732899
Test: atest SystemDreamTest
Test: verified fingerprint unlock during dream works
Test: verified dream start/stop broadcasts are sent correctly
Change-Id: Ibcd8b8b00b855bfc52a295e2663926e55d664a69

services/core/java/com/android/server/dreams/DreamController.java

@@ -240,6 +240,7 @@ final class DreamController {
 
                 if (mSentStartBroadcast) {
                     mContext.sendBroadcastAsUser(mDreamingStoppedIntent, UserHandle.ALL);
+                    mSentStartBroadcast = false;
                 }
 
                 mListener.onDreamStopped(dream.mToken);