X64-Bug in TGpHugeFile

```
In Unit GpHugeF.pas

the method OffsetPtr calculate a address in DWORD. This will fail in x64 and
high pointers.

Suggestion is ...

function OffsetPtr(ptr: pointer; offset: DWORD): pointer;
begin
//BUG Result := pointer(DWORD(ptr)+offset);
Result := pointer(NativeUInt(ptr)+offset);
end; { OffsetPtr }

```

Original issue reported on code.google.com by `mxxa2a...@gmail.com` on 25 Mar 2015 at 8:48

Start in Unit GpHugeF.pas and inspect the OffsetPtr method, especially its DWORD-based address calculation and the suggested NativeUInt alternative. Done means OffsetPtr preserves high pointer addresses on x64; verify this against the unit's available build or validation process.

Written by the indexing model from the issue text.