pgsql: Add sentinel_ok() check to BumpCheck().

Add sentinel_ok() check to BumpCheck().

Effectively an oversight in 29f6a959cf. The code went to the trouble of
doing set_sentinel() but no code ever checked it was still set during
BumpCheck(). Since bump context types are used in a handful of places,
it very much makes sense to backpatch this to where bump.c was added so we
can more easily discover any memory stomping bugs.

Reported-by: shihao zhong <zhong950419(at)gmail(dot)com>
Author: David Rowley <dgrowleyml(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAGRkXqQxTCthDEnw_10OEGLVNMUeyE4So-K29jmn9nAkxtr1ow@mail.gmail.com
Backpatch-through: 17

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/86848d19bdbbf0daac6ca1b92a8885179cae8db5

Modified Files
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src/backend/utils/mmgr/bump.c | 4 ++++
1 file changed, 4 insertions(+)