Make sure linked and linked_conn can't get out of sync
In legacy/trac#21576 (moved), we encountered a situation where linked is true, but linked_conn is NULL.
This shouldn't happen, so we need to diagnose the error, and fix it.
In legacy/trac#21576 (moved), we encountered a situation where linked is true, but linked_conn is NULL.
This shouldn't happen, so we need to diagnose the error, and fix it.