Fix TextBox wrapping.
Fix TextBox wrapping.

Fixes issue #475

jazzay/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,MrDaedra/Avalonia,AvaloniaUI/Avalonia,akrisiun/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,susloparovdenis/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,Perspex/Perspex,susloparovdenis/Perspex,SuperJMN/Avalonia,susloparovdenis/Perspex,susloparovdenis/Avalonia,wieslawsoltes/Perspex,OronDF343/Avalonia,AvaloniaUI/Avalonia,MrDaedra/Avalonia,AvaloniaUI/Avalonia,punker76/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,wieslawsoltes/Perspex,grokys/Perspex,Perspex/Perspex,jkoritzinsky/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,OronDF343/Avalonia,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,SuperJMN/Avalonia,grokys/Perspex,AvaloniaUI/Avalonia