Don't add DEFAULT_BG if other backgrounds found
Don't add DEFAULT_BG if other backgrounds found

This fixes an issue I have been having locally, that I have one image in /usr/share/backgrounds/ that I update daily.

If you only have one image in /usr/share/backgrounds, and you want lightdm to display that image, it would switch randomly between your image and the DEFAULT_BG.

DEFAULT_BG is already returned in getBackgrounds() if no background was defined or found, so adding it in backgrounds() makes not much sense, since that way `localStorage.getItem('background')` is always already set and the "or" case never actually happens

Litarvan/lightdm-webkit-theme-litarvan,Litarvan/lightdm-webkit-theme-litarvan,Litarvan/lightdm-webkit-theme-litarvan