pgsql: Fix crash of pg_stat_statements_info() without library loaded

Fix crash of pg_stat_statements_info() without library loaded

Other code paths are already protected against this case, and _PG_init()
warns about that in pg_stat_statements.c.  While on it, I have checked
the other extensions of the tree but did not notice any holes.

Oversight in 9fbc3f3.

Author: Jaime Casanova
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/CAJKUy5gF4=_=qhJ1VX_tSGFfjKHb9BvzhRYWSApJD=Bfwp2SBw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bca96ddab57c7c64ce442b0f9f35558741c7f8bd

Modified Files
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contrib/pg_stat_statements/pg_stat_statements.c | 5 +++++
1 file changed, 5 insertions(+)