New created user can accept same invitation twice at GUI

[oguzcankirmemis]

After the second accept, I get the error FatalError: Invitation does not exist, and then the server crashes.

Steps to reproduce:
-Start the dashboard
-Add 2 users
-From one user create an account and send to other user a invitation
-Login to other user with GUI
-Click to accept invitation insteaded of create an account
-Now go to messages and accept the same invitation again

Note that this does not work other way around, if you first accept the invite at the messages, than page will redirect you to the dashboard. The problem is that changeInviteStatus does not reload the whole page, but changes the account (so messages inbox does not get reloaded).