fix zrangebyscore bug

[mytrygithub]

fix zrangebyscore score -inf and +inf bug
note：merge blackwidow

[mytrygithub]

check:

host>zadd mzset -inf a -inf b -1 c 2 d 3 e +inf f +inf g
(integer) 7
host>zrevrangebyscore mzset inf -inf WITHSCORES
 1) "g"
 2) "inf"
 3) "f"
 4) "inf"
 5) "e"
 6) "3"
 7) "d"
 8) "2"
 9) "c"
10) "-1"
11) "b"
12) "-inf"
13) "a"
14) "-inf"
host> zrangebyscore mzset -inf +inf WITHSCORES
 1) "a"
 2) "-inf"
 3) "b"
 4) "-inf"
 5) "c"
 6) "-1"
 7) "d"
 8) "2"
 9) "e"
10) "3"
11) "f"
12) "inf"
13) "g"
14) "inf"
host> 

[rockeet]

This PR fixed issue #8