Fixes UITextInput::getSelectionText()
Fixes UITextInput::getSelectionText()

Fixes issue #186

There were some semantical errors with its implementation. Rewrote most of the function using a more concise and intuitive algorithm.

mcanthony/Polycode,fodinabor/Polycode,GovanifY/Polycode,ivansafrin/Polycode,Xetlin/Lua,sshaileshk/Polycode,cartman300/Polycode,fodinabor/Polycode,mcanthony/Polycode,cartman300/Polycode,thorsummoner/polycode,ivansafrin/Polycode,carlosmarti/Polycode,fodinabor/Polycode,zeebok/Polycode,thorsummoner/polycode,thorsummoner/polycode,mcanthony/Polycode,Xetlin/Lua,thorsummoner/polycode,GovanifY/Polycode,cartman300/Polycode,hksonngan/Polycode,fodinabor/Polycode,sshaileshk/Polycode,sshaileshk/Polycode,carlosmarti/Polycode,cartman300/Polycode,Xetlin/Lua,Xetlin/Lua,ivansafrin/Polycode,mcanthony/Polycode,carlosmarti/Polycode,hksonngan/Polycode,hksonngan/Polycode,zeebok/Polycode,GovanifY/Polycode,sshaileshk/Polycode,zeebok/Polycode,hksonngan/Polycode,zeebok/Polycode,GovanifY/Polycode,ivansafrin/Polycode