Fix tuto3 picture taken crash on all devices

A modification of the JavaCameraView is needed to avoid a crash when the
app is exited. It is a good practice to remove the callback after the
stopPreview method.

modules/java/generator/src/java/android+JavaCameraView.java

@@ -179,6 +179,8 @@ public class JavaCameraView extends CameraBridgeViewBase implements PreviewCallb
         synchronized (this) {
             if (mCamera != null) {
                 mCamera.stopPreview();
+                mCamera.setPreviewCallback(null);
+
                 mCamera.release();
             }
             mCamera = null;