preprocessBuffers( bufferHeaders = [] ) {

		for ( let i = 0; i < bufferHeaders.length; i ++ ) {

			const bufferHeader = bufferHeaders[ i ];
			bufferHeader.isActive = false;
			bufferHeader.isExternal = !! bufferHeader.uri;

		}
		return bufferHeaders;

	}
Iterate over the list of buffers from the subtree JSON and add the isActive field for easier parsing later.
This modifies the objects in place.
@param {Object[]} [bufferHeaders=[]] The JSON from subtreeJson.buffers.
@returns {BufferHeader[]} The same array of headers with additional fields.
@private