Fix the table top line on some pages from the Invitation app

Steps to reproduce:

1. Set your SMTP server for the Invitation app: http://localhost:8080/xwiki/bin/admin/XWiki/XWikiPreferences?editor=globaladmin&section=Invitation
2. Go to Invitation.WebHome and send 2 invites: accept one and leave the other Pending
3. Go to http://localhost:8080/xwiki/bin/view/Invitation/InvitationMemberActions?inspect=all -> notice how the top line is broken
4. Click on the Pending Invitation -> again notice how the top line isn't properly displayed

Doesn't reproduce if you click on these other types of Invitations: Accepted, Declined or "Failed to send message".