pgsql: Fix use-after-release mistake in currtid() and currtid2() for vi

Fix use-after-release mistake in currtid() and currtid2() for views

This issue has been present since the introduction of this code as of
a3519a2 from 2002, and has been found by buildfarm member prion that
uses RELCACHE_FORCE_RELEASE via the tests introduced recently in
e786be5.

Discussion: https://postgr.es/m/[email protected]
Backpatch-through: 9.5

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a36f216209b818a28d7597966032cc3dce6acfa2

Modified Files
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src/backend/utils/adt/tid.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)