iStore Cart sharing functionality does not work with Multicustomer Access feature

Problem Description

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Below steps explains the problem:-

1) iStore User A has Multicustomer Access to Customer Accounts 123 and 456

2) iStore User A's default Party is Customer Account 123

3) iStore User B has access to only Customer Account 456

4) iStore User B tries to share cart with Customer A, but cannot see Customer A's contact listed in the Share Cart page

5) iStore User A now switches default party to Customer Account 456 (through iSupport Admin)

6) Now, Customer B is able to see and share cart with Customer A

Ideally, Customer B should be able to share cart with Customer A, no matter which Customer Account is set as default for Customer A