Fix for decodeEntities when parsing an html string in parts

[koalas11]

when diving the string in TestData.kt in two string, if i parse those string like this:

ksoupHtmlParser.write(TestData.htmlStringPart1)
ksoupHtmlParser.write(TestData.htmlStringPart2)
ksoupHtmlParser.end()

it will throw an exception because the buffer has only the second string but the index are starting from the first string

[MohamedRejeb]

Thanks for your contribution.