pgsql: radixtree: Fix SIGSEGV at update of embeddable value to non-embe

radixtree: Fix SIGSEGV at update of embeddable value to non-embeddable.

Also, fix a memory leak when updating from non-embeddable to
embeddable. Both were unreachable without adding C code.

Reported-by: Noah Misch
Author: Noah Misch
Reviewed-by: Masahiko Sawada, John Naylor
Discussion: https://postgr.es/m/20240424210319.4c.nmisch%40google.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bb7f195ff78851e5fcee7230108a16d70be13579

Modified Files
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src/include/lib/radixtree.h                        |   6 +-
.../test_tidstore/expected/test_tidstore.out       | 116 ++++++++++++++++++++-
.../modules/test_tidstore/sql/test_tidstore.sql    |  21 +++-
src/test/modules/test_tidstore/test_tidstore.c     |  15 +++
4 files changed, 148 insertions(+), 10 deletions(-)