RDPDR file size may be truncated to 32 bits

RDPDR uses 64-bit integers to represent file size, but Guacamole's RDP filesystem structure only uses a standard int for this. C's int is very likely to be 32-bit, even on 64-bit systems, causing the file size to be truncated for sufficiently large files (2G+).

Guacamole's RDP filesystem structure should be modified to be consistent with RDPDR and use 64-bit integers to represent file size.