fix string to double conversion, stopped parsing on \0 even if the string has more data.

getLongLongFromObject calls string2ll which has this line:
/* Return if not all bytes were used. */
so if you pass an sds with 3 characters "1\01" it will fail.

but getLongDoubleFromObject calls strtold, and considers it ok if eptr[0]==`\0`
i.e. if the end of the string found by strtold ends with null terminator

127.0.0.1:6379> set a 1
OK
127.0.0.1:6379> setrange a 2 2
(integer) 3
127.0.0.1:6379> get a
"1\x002"
127.0.0.1:6379> incrbyfloat a 2
"3"
127.0.0.1:6379> get a
"3"
