Custom login image broken if FQDN for auth differs from the one used to reach webapp

Steps to reproduce:

• Set custom login image using webtop release "wt-5.9.2" or below
• Check that custom image is correctly displayed in landing page
• Change internet name field in Domain data
• Check login image again

Expected behaviour:

• Custom login image is shown as previous

Actual behaviour:

• No customization visible, default image is displayed