c70f321c6f added an extra check if KS
exists. This check can throw `data_dictionary::no_such_keyspace`
exception, which is supposed to be caught and a more user-friendly
exception should be thrown instead.
This commit fixes the above problem and adds a testcase to validate it
doesn't appear ever again.
Also, I moved the check for the keyspace outside of the `for` loop, as
it doesn't need to be checked repeatedly.
Additionally, I added an extra comment to both `no_such_keyspace` and
`no_such_column_family` exceptions explaining they should not be
returned directly to the caller, as they lack error code, which may not
trigger correct exceptions handling mechanisms on the driver side.
Fixes: #20097
(cherry picked from commit f1e8976fbe)
Closesscylladb/scylladb#20553
b60f9ef4c2