Bug fix: signature max size not working

I've just fixed an error that a few of you have been running into: the create signature page where you choose a custom BG image, was not saying the file size was too big (if it was). Instead, the page would just reload with no error. On that note, no error was ever showing up when it should have been. This is now fixed.

Thanks! I had that problem last night trying to add Dizeth's signature. It took several times of me decreasing the file size to finally get it to work.