do not disable the radio button in the avatar selection modal

You can now select the second radio button even though you haven't uploaded a custom avatar yet.
When you select it, the save button will be disabled until you upload a picture.

![profile_-_zogstrip_-_discourse](https://f.cloud.github.com/assets/362783/997040/d020b6e4-09da-11e3-8215-1fd97df21372.png)