Bug in Diff.pas comparing characters.

Hi Jesús

The diff.pas from Jedi code format has a bug when comparing strings.I had not corrected it since we do not use it in JCF and it does not affect us.

Now I backported the change from the original source of Diff.pas [TextDiff]https://github.com/rickard67/TextDiff)

Also you can see [lazarus forum]https://forum.lazarus.freepascal.org/index.php/topic,62219.30.html)

The bug is in Execute function comparing chars. String are 1 based.

    //finally, append any trailing matches onto compareList ...
    with FLastCompareRec do
    begin
-     AddChangeChr(oldIndex1,len1Minus1-oldIndex1, ckNone);
+     AddChangeChr(oldIndex1,len1Minus1-oldIndex1+1, ckNone);
    end;
  finally
    FExecuting := false;

You are doing an awesome work with this git wrapper.

Saludos Domingo.