Redis Possible optimization in t_hash.c: hashTypeSet()

In hashTypeSet() function, we first use dictFind() to look for the field and if it does not exist, we use dictAdd() to add it. In dictAdd() the dictionary will look for the field again and I think this procedure is meaningless as we already know that the field does not exist.

An optimization is to use dictAddRaw() instead of dictFind() and dictAdd(). If we use dictAddRaw(), a new entry will be added when the field does not exist, and what we should do then is just set the value of that entry, and set its key to 'sdsdup(field)' in the case that 'HASH_SET_TAKE_FIELD' flag wasn't set.