[Cairo] Fixed wrong index calculation of text in case text contains Unicode chars
[Cairo] Fixed wrong index calculation of text in case text contains Unicode chars

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