Ensure `old_interface` is always set before return
Ensure `old_interface` is always set before return

Otherwise if we leave the method in the early return, it will be
unintentionally set to nil.

deivid-rodriguez/byebug,yui-knk/byebug,deivid-rodriguez/byebug,deivid-rodriguez/byebug,yui-knk/byebug,yui-knk/byebug