expand "offset > existing_size" case to return data written, not bytes
expand "offset > existing_size" case to return data written, not bytes

Before, sqlfs_proc_write() was returning the total number of bytes written
when it had to write blank bytes because of offset.  FUSE expects it to
just return how many bytes of actual data it wrote, not the blank stuff too

guardianproject/libsqlfs,spthaolt/libsqlfs,guardianproject/libsqlfs,eighthave/libsqlfs,spthaolt/libsqlfs,eighthave/libsqlfs,guardianproject/libsqlfs,eighthave/libsqlfs,eighthave/libsqlfs,spthaolt/libsqlfs,guardianproject/libsqlfs,spthaolt/libsqlfs,guardianproject/libsqlfs,spthaolt/libsqlfs,eighthave/libsqlfs