Can't update profile when max number of username changes reached

[ffont]

This was reported by a user through our support channel. Apparently the use reached the maximum number of times username can be changed and since then she can't update the profile because clicking "save" triggers the "max number of username changes" error. I have not tried to reproduce the error so far. I think this eventuality was contemplated when implementing the username change feature, but I can't be 100% sure now.