Fix stderr reporting when special cursor line isn't found

An easy way to reproduce this issue is to run the plugin with an old
version of pasfmt from before the `--cursor` option was added. In this
case it will tell you an error occurred but won't be able to tell you
anything about it.

Author: zaneduffield

Pasfmt.FormatCore.pas

@@ -40,6 +40,7 @@ function ExtractCursorTag(Data: string; out TagValue: string): string;
   StartPos: Integer;
   EndPos: Integer;
 begin
+  Result := Data;
   TagPos := System.Pos(CTag, Data);
   if TagPos > 0 then begin
     StartPos := TagPos + Length(CTag);