Checkin of item with requests: in transit to wrong library

[pronguen]

Describe the issue
As a librarian, in a patron account, I do a checkin of an item that holds a request:

1. If the item is requested with a pickup location not equal to my library, the item goes "at desk" instead of "in transit"
2. If the item is requested with a pickup location equal to my library, the item goes "in transit" to a random library (?) instead of "at desk".

As a librarian, in the checkin form, the same transactions have different behaviour:

1. If the item is requested with a pickup location not equal to my library, the item goes "in transit" to a random library (?) instead of "in transit" to the pickup library.
2. If the item is requested with a pickup location equal to my library, the item goes "in transit" to a random library (?) instead of "at desk".

All cases have been tested on ilsdev and ilspilot

To Reproduce

1. Open a patron account (tab checkout)
2. Add for this patron 2 items on loan
3. Add requests to these 2 items, one with pickup location equal to librarian's library, the other with another pickup location (for this step you have to log in as a patron)
4. In the patron account (tab checkout), checkin the 2 items
5. See error

Reproduce the same processes, but do the checkin on the 2 items from the checkin form (outside of a patron account).

Expected behavior

• the result of a checkin should always be the same, whenever it is in the checkin form or in the patron account (tab checkout)
• the transit destination should be the pickup library name (ideally "pickup location name") of the request
• status "in transit" or "at desk" should correspond to the transaction library (ie. to the library of the connected librarian)

Software version
ilsdev + ilspilot
rero-ils version c236bc8
rero-ils-ui version 4fc4656d

[BadrAly]

An invenio-circulation bug related to this function https://github.com/inveniosoftware/invenio-circulation/blob/c3fcc1a4674d5df24221e3c068e8e0c07db68016/invenio_circulation/transitions/transitions.py#L80

The current behaviour: a document with multiple items (for example 5 items) and each item has a different request (total of 5 requests). Assume that the first item is already checked-out to a non-requested patron. (total of loans on document = 6 -> 5 requests and one checkout)
Try to check-in the checked-out item, the system will then attach the remaining 5 requests(loans) to the checked-in item.