[YCQL] Logging into a role without password will crash tserver.

[WesleyW]

After enabling YCQL authentication, I tried creating a role with login=true and no password. Creation worked but attempting to log in with the role will crash the tserver.
Steps:

• bin/yb-ctl start --tserver_flags=use_cassandra_authentication=true
• bin/cqlsh -u cassandra -p cassandra
• create role testing with login=true;
• select * from system_auth.roles shows correct roles.
• exit
• bin/cqlsh -u testing will prompt for a password and then crash after any input.

tserver fatal log:

F1003 13:18:14.812242 268431360 ql_value.h:113] Check failed: pb_.has_string_value() 

Looks like a failed null check since password is recorded as null.

[hectorgcr]

This has been closed by 65d3cc7 and duplicate of #4459