pgsql: Fix alignment in multirange_get_range() function

Fix alignment in multirange_get_range() function

The multirange_get_range() function fails when two boundaries of the same
range have different alignments.  Fix that by adding proper pointer alignment.

Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/17300-dced2d01ddeb1f2f%40postgresql.org
Backpatch-through: 14

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7615edd1db92b0bf909037480e8d9fcdb1be5f4b

Modified Files
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src/backend/utils/adt/multirangetypes.c       |  3 +++
src/test/regress/expected/multirangetypes.out | 21 +++++++++++++++++----
src/test/regress/expected/rangetypes.out      |  6 ------
src/test/regress/sql/multirangetypes.sql      |  4 +++-
src/test/regress/sql/rangetypes.sql           |  1 -
5 files changed, 23 insertions(+), 12 deletions(-)