pgsql: Fix thinko when ending progress report for a backend

Fix thinko when ending progress report for a backend

The logic ending progress reporting for a backend entry introduced by
b6fb647 causes callers of pgstat_progress_end_command() to do some extra
work when track_activities is enabled as the process fields are reset in
the backend entry even if no command were started for reporting.

This resets the fields only if a command is registered for progress
reporting, and only if track_activities is enabled.

Author: Masahiho Sawada
Discussion: https://postgr.es/m/CAD21AoCry_vJ0E-m5oxJXGL3pnos-xYGCzF95rK5Bbi3Uf-rpA@mail.gmail.com
Backpatch-through: 9.6

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f4b91a50e9e6757679322c454916bcd6b1dcbc15

Modified Files
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src/backend/postmaster/pgstat.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)