Fix background image upload too big feedback
Fix background image upload too big feedback

It used to be inconsistent about whether or not the custom background
setting succeeded.

QuiteQuiet/Pokemon-Showdown-Client,submindraikou/Pokemon-Showdown-Client,asgdf/Pokemon-Showdown-Client,asgdf/Pokemon-Showdown-Client,Zarel/Pokemon-Showdown-Client,panpawn/Gold-Client,QuiteQuiet/Pokemon-Showdown-Client,Zarel/Pokemon-Showdown-Client,sirDonovan/Pokemon-Showdown-Client,QuiteQuiet/Pokemon-Showdown-Client,QuiteQuiet/Pokemon-Showdown-Client,panpawn/Gold-Client,sirDonovan/Pokemon-Showdown-Client,submindraikou/Pokemon-Showdown-Client,asgdf/Pokemon-Showdown-Client,sirDonovan/Pokemon-Showdown-Client,panpawn/Gold-Client,submindraikou/Pokemon-Showdown-Client,asgdf/Pokemon-Showdown-Client,sirDonovan/Pokemon-Showdown-Client,Zarel/Pokemon-Showdown-Client,Zarel/Pokemon-Showdown-Client