rdb.c/rdbLoadObject: convert type when needed before pushed to a ziplist

Small Changes:
1.Convert type when needed before pushed to a ziplist, this can be more efficient when the `field` or `value` is very long, as we can spare the realloc and copy time.
2.Mind for the edge case of get rdb version.

        eg: printf("%d\n",atoi(" 03a"));  -> 3

3.When the type is `REDIS_RDB_OPCODE_EOF` or `REDIS_RDB_OPCODE_SELECTDB`, and `expiretime` is not -1, a wrong type error may happen.