Only check barcode if we need to

Currently, the robot will pause briefly on the way to load to check the pin barcode. The barcode is only useful to user who have actually set the expected barcode in ispyb and so synchweb can tell them if it matches. Therefore if there is no expected barcode in ispyb then we do not need to check the barcode of the pin.

## Acceptance Criteria
* Agamemnon tells us the expected barcode (currently it doesn't)
* Based on this we set the robot to not check the barcode (PV for this exists)