Bug 37551: (24.05.x) Only delete price when there is already an itemprice

Bug 37551: (24.05.x) Only delete price when there is already an itemprice

To test:
1. Have a mrc file with some different prices. In my case I am using the mrc file attached here with different price values in the 975$p and 975$a
2. Set the MarcFieldsToOrder to "price: 975$p" and  MarcItemFieldsToOrder to "price: 975$a"
3. In Acquisitions create a new basket > add to basket > from a new file
4. The value from MarcFieldsToOrder (975$p) is always set as the price when it should be the value from MarcItemFieldsToOrder (975$a)
5. APPLY PATCH, restart_all
6. Try steps 1 - 3 again, this time item price should be correctly handled.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>