UI error when parent process instance details have been removed

For a process instance with the following characteristics:

• There is a parent/child process relationship
• The sub-process instance is defined with Independent=true, Wait for Completion=false
• The parent process is ended
• The audit log data of the parent process has been removed by the LogCleanupCommand

the following problems show up in the process instance detail view:

1. The UI shows a "Could not find process instance with id "1"" popup error
2. The Diagram tab does not show the process diagram

The UI should handle this situation gracefully - if the parent process instance details can no longer be accessed, then the link should be replaced by just a simple text node, and no error popup should be shown. The diagram should be displayed without support of linking to the parent process instance.