pgsql: Fix vacuum_cost_delay check for balance calculation.

Fix vacuum_cost_delay check for balance calculation.

Commit 1021bd6a89 excluded autovacuum workers from cost-limit balance
calculations when per-relation options were set. The code checks for
limit and cost_delay being greater than zero, but since cost_delay can
be set to -1 the test needs to check for greater than or zero.

Backpatch to all supported branches since 1021bd6a89 was backpatched
all the way at the time.

Author: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Reviewed-by: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Discussion: https://postgr.es/m/CAD21AoBS7o6Ljt_vfqPQPf67AhzKu3fR0iqk8B=vVYczMugKMQ@mail.gmail.com
Backpatch-through: v11 (all supported branches)

Branch
------
REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/cba3c8f6dd7fffb63eac2f31d98bd23816959d04

Modified Files
--------------
src/backend/postmaster/autovacuum.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)