XLM to JSON migration locked if Jira is restarted during a migration

How to reproduce

• Launch a XML to JSON migration job
• Shutdown Jira before the migration job is completed
• Start Jira
• Go top "Elements Administration" -> "System" tab

Current Result

• The migration button is disabled
• The progress bar is blocked in 0%

Expected

• Information about the last migration are displayed
• The migration button is enabled and the migration can be restarted