JavaCameraView now handles a null attribute parameter.

This commit avoid a null pointer exception if the view attributes are null. 
Xml attributes exist if the view is created in with an Android Xml resource. Some developers needs to create a View directly on java and not in xml (which means that the AttributeSet param is null).

According to https://github.com/Itseez/opencv/pull/842, I have removed the tabs and converted them to spaces. Thank you for the advice about the other constructor.