Returns the string length of the value associated with field in the hash stored at key. If the key or the field do not exist, 0 is returned.
@return
@integer-reply: the string length of the value associated with field, or zero when field is not present in the hash or key does not exist at all.
@examples
HMSET myhash f1 HelloWorld f2 99 f3 -256
HSTRLEN myhash f1
HSTRLEN myhash f2
HSTRLEN myhash f3