FileRStream abstracts the low-level functions open, close, read and lseek to the user.
vtablePtr+4: file handle
vtablePtr+10: pointer unknown *((_BYTE *)vtablePtr + 10)
vtablePtr[1]=status
3: set in closeCurrentFile if file closed successfully or read fails and errno is 0
5: set in closeCUrrentFIle if close failed
1: set in openFile if open fails, or if read fails and errno is present
0: set in openFile if open worked, or in seekToPos when status was 2 before
2: set in read if readlen!=target len