pgsql: Don't prematurely free the BufferAccessStrategy in pgstat_heap()

Don't prematurely free the BufferAccessStrategy in pgstat_heap().

This function continued to use it after heap_endscan() freed it.  In
passing, don't explicit create a strategy here.  Instead, use the one
created by heap_beginscan_strat(), if any.  Back-patch to 9.2, where use
of a BufferAccessStrategy here was introduced.

Branch
------
REL9_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/37a4d3d70617f574b9a3dd5af079430b24817333

Modified Files
--------------
contrib/pgstattuple/pgstattuple.c |   13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)