pgsql: Don't reset relhasindex for partitioned tables on ANALYZE

Don't reset relhasindex for partitioned tables on ANALYZE

Commit 0e69f705cc1a introduced code to analyze partitioned table;
however, that code fails to preserve pg_class.relhasindex correctly.
Fix by observing whether any indexes exist rather than accidentally
falling through to assuming none do.

Backpatch to 14.

Author: Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>
Reviewed-by: Álvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Reviewed-by: Zhihong Yu <zyu(at)yugabyte(dot)com>
Discussion: https://postgr.es/m/CALNJ-vS1R3Qoe5t4tbzxrkpBtzRbPq1dDcW4RmA_a+oqweF30w@mail.gmail.com

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/be280cdad2985749e558212b0a5c8bdf9abb4e6a

Modified Files
--------------
src/backend/commands/analyze.c | 32 +++++++++++++++++++++++---------
src/test/regress/expected/vacuum.out | 22 ++++++++++++++++++++++
src/test/regress/sql/vacuum.sql | 16 ++++++++++++++++
3 files changed, 61 insertions(+), 9 deletions(-)