Version related JQL functions do not gracefully handle versions associated with not existing projects

Under normal operation, all Version s should be associated with an existing Project. It's possible to quite easily introduce a data integrity issue by for example deleting a Project via ProjectManager which unlike ProjectService does not also remove the Version s associated with the project being removed.

If a Version which is not associated with an existing Project exists in the instance then releaseDate(), startDate() and overdue() JQL functions fail with a NullPointerException and no issues are ever returned from queries which use them.