Minimal fix for incorrect no-op condition

If you set the output using MSG_SET_OUTPUT_BUFFER_RENDERER and
then clear the output using MSG_SET_SURFACE, or vice-versa, the
second message should not be turned into a no-op.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139452462

extensions/vp9/src/main/java/com/google/android/exoplayer/ext/vp9/LibvpxVideoTrackRenderer.java

@@ -446,7 +446,7 @@ public void handleMessage(int messageType, Object message) throws ExoPlaybackExc
   }
 
   private void setSurface(Surface surface) {
-    if (this.surface == surface) {
+    if (this.surface == surface && outputBufferRenderer == null) {
       return;
     }
     this.surface = surface;
@@ -459,7 +459,7 @@ private void setSurface(Surface surface) {
   }
 
   private void setOutputBufferRenderer(VpxOutputBufferRenderer outputBufferRenderer) {
-    if (this.outputBufferRenderer == outputBufferRenderer) {
+    if (this.outputBufferRenderer == outputBufferRenderer && surface == null) {
       return;
     }
     this.outputBufferRenderer = outputBufferRenderer;