Update PHPTextFileIO.php

Check if $bufferSize into setBufferSize function it's a positive number to read
Merge pull request #1 from Grimpow/patch-1

Update PHPTextFileIO.php
Improved some methods
Merge branch 'master' of https://github.com/enunez80/PHPTextFileIO

Conflicts:
	PHPTextFileIO.php
Update PHPTextFileIO.php