pgsql: Minor improvements for waitlsn.c

Minor improvements for waitlsn.c

 * Remove extra includes
 * Fill 'cur' in addLSNWaiter() before taking the spinlock
 * Initialize 'endtime' with zero in WaitForLSN() to avoid compiler warning

Reported-by: Alvaro Herrera, Masahiko Sawada, Daniel Gustafsson
Discussion: https://postgr.es/m/202404030658.hhj3vfxeyhft%40alvherre.pgsql
Discussion: https://postgr.es/m/CAD21AoAx7irptnPH1OkkkNh9E0M6X-phfX7sYZfwoMsc1qV1sQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e37662f22158c29bc55eda4eda1757f444cf701a

Modified Files
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src/backend/commands/waitlsn.c | 18 ++++--------------
1 file changed, 4 insertions(+), 14 deletions(-)