function getMessageHeader(aMessageIndices, oMessageObject) {
		oMessageObject = oMessageObject ?? oCurrentMessages;
		return {
			"sap-message": oMessageObject.buildString(aMessageIndices)
		};
	}
Creates a response header object containing only a <code>sap-message</code> property for
the given messages.

@param {number[]} [aMessageIndices]
  The indices of messages to be used in the <code>sap-message</code> header; if not given,
  all current messages are used
@param {object} [oMessageObject=oCurrentMessages]
  The current oMessageObject
@returns {object}
  A response header object containing the <code>sap-message</code> property for the given
  messages