vdfuse fails on extended partitions

Binary package hint: virtualbox-ose

When attempting to use vdfuse to mount a .vdi containing extended partitions, it fails with "Invalid EBR signature found on image".

To reproduce:
- Download attached overflow.vdi.xz, decompress with 'xz -d overflow.vdi.xz'
- Try to mount it: 'mkdir mnt; vdfuse -f overflow.vdi mnt'
- Error is printed and vdfuse fails

The error occurs because in vdfuse.c initialisePartitionTable() line 430, the read is offset by EBR_START, but the struct EBRentry already contains padding to take care of that. Also on line 444, uOffset should be the EBR offset in bytes, but it is assigned ebr.chain.offset, which is expressed in sectors.

I shall attach a patch to fix these bugs.