Fixing buffer position change after reading

It seems that only place where we use the buffer for appending is ASCII buffer in SCP code, where ForceLen is true, so the bug would not happen - as Len == Result.

Source commit: d30cccffcba704e0502005721149b50964cf5a7c

source/core/FileBuffer.cpp

@@ -79,7 +79,7 @@ DWORD __fastcall TFileBuffer::ReadStream(TStream * Stream, const DWORD Len, bool
     {
       Size = Size - Len + Result;
     }
-    FMemory->Seek(Len, soCurrent);
+    FMemory->Seek(Result, soCurrent);
   }
   catch(EReadError &)
   {