Assert while autovacuum was executing

Hi,

I have been testing 16beta1, last commit
a14e75eb0b6a73821e0d66c0d407372ec8376105
I just let sqlsmith do its magic before trying something else, and
today I found a core with the attached backtrace.

Only information on the log was this:

DETAIL:  Failed process was running: autovacuum: VACUUM
public.array_index_op_test

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Jaime Casanova
Director de Servicios Profesionales
SYSTEMGUARDS - Consultores de PostgreSQL