Forget to enable encoding thread on camera switch

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

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

@@ -257,6 +257,7 @@ public class SrsPublisher {
         } else {
             mEncoder.setCameraFrontFace();
         }
+        mCameraView.enableEncoding();
         mCameraView.startCamera();
     }