cql3: Fix crash when parsing collection condition
cql3: Fix crash when parsing collection condition

Happened when parsing a statement like this:

 DELETE FROM tmap WHERE k=0 IF m[null] = 'foo'

Message-Id: <02b3ef8b9d29715d8df57f9d2564f84e8cbb1e37@scylladb.com>

duarten/scylla,raphaelsc/scylla,duarten/scylla,avikivity/scylla,raphaelsc/scylla,kjniemi/scylla,scylladb/scylla,kjniemi/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,kjniemi/scylla,scylladb/scylla