row: append(): downgrade assert to on_internal_error()
row: append(): downgrade assert to on_internal_error()

This assert, added by 060e3f8 is supposed to make sure the invariant of
the append() is respected, in order to prevent building an invalid row.
The assert however proved to be too harsh, as it converts any bug
causing out-of-order clustering rows into cluster unavailability.
Downgrade it to on_internal_error(). This will still prevent corrupt
data from spreading in the cluster, without the unavailability caused by
the assert.

Fixes: #5786
Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Message-Id: <20200211083829.915031-1-a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla