Fix empty string zset test
Fix empty string zset test

The test was tampered to make it pass ignoring the fact that empty strings
were broken. Fixing empty strings made the test fail as expected. Restore the
test as it should be.

seppo0010/rlite,pombredanne/rlite,jqk6/rlite,pombredanne/rlite,jqk6/rlite,seppo0010/rlite,seppo0010/rlite