Wrap around fix - Range Check Error

[superflexible]

Because FStart sometimes equaled the buffer size, a Range Check Error could occur. Fixed.

There are two places in the source where I needed to add:
if FStart=Size then
FStart:=0;

Unfortunately the pull request contains some additional "changes" due to German umlauts, sorry for that!

[MHumm]

Thanks for providing this fix. But before I can accept it we need to check two things:

1. Does it pass the existing unit tests?
2. Are further unit tests are necessary to check for this failure and that it is fixed?

It would be really nice if you could do these. I also don't know why you have such issues with our lovely German umlauts. Maybe the files are still ANSI. If yes, I'll change them to UTF8 after accepting your pull request.

[superflexible]

Hi,
OK I will try the unit tests.

The umlaut thing happened because I edited the file directly in the GithHub web site. I think it converted it to UTF-8.