Add condition before pushing to the encoder

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

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

@@ -120,13 +120,15 @@ public class SrsCameraView extends GLSurfaceView implements GLSurfaceView.Render
         surfaceTexture.getTransformMatrix(mSurfaceMatrix);
         Matrix.multiplyMM(mTransformMatrix, 0, mSurfaceMatrix, 0, mProjectionMatrix, 0);
         magicFilter.setTextureTransformMatrix(mTransformMatrix);
-
         magicFilter.onDrawFrame(mOESTextureId);
+
+        if (worker != null) {
             mGLIntBufferCache.add(magicFilter.getGLFboBuffer());
             synchronized (writeLock) {
                 writeLock.notifyAll();
             }
         }
+    }
 
     public void setPreviewCallback(PreviewCallback cb) {
         mPrevCb = cb;