Warnings are being cleared after every query

[kuba--]

If you send two queries in the same session, e.g.:

-- some empty query as a comment;

SHOW WARNINGS;

We expect to see a warning(s). At least:
query was empty after trimming comments, so it will be ignored.

Unfortunatelly we have a rule clearWarnings:

go-mysql-server/sql/analyzer/rules.go

Line 47 in 7beeb8d

{"clear_warnings", clearWarnings},

which runs after every query. That's why the second query show warning has a cleared session.