compound: Throw exception when key is too large rather than abort
compound: Throw exception when key is too large rather than abort

Abort is too big of a hammer.

Refs #809.

Message-Id: <75d897cdfc911daf2bd485462d2349c4be8b2bf5@scylladb.com>

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