Fix off-by-one bug in writing test.
Fix off-by-one bug in writing test.

It claimed to write TESTSIZE bytes, but was writing TESTSIZE-1, now it writes
TESTSIZE bytes.

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