Forget to enable encoder on camera switch

Signed-off-by: Leo Ma <begeekmyfriend@gmail.com>

library/src/main/java/net/ossrs/yasea/SrsPublisher.java

@@ -218,6 +218,7 @@ public class SrsPublisher {
             } else {
                 mEncoder.setCameraFrontFace();
             }
+            mCameraView.enableEncoding();
             mCameraView.startCamera();
         }
     }