pgsql: Fix potential for compiler warning in GlobalVisTestFor().

Fix potential for compiler warning in GlobalVisTestFor().

In d9d8aa9bb9a I added a defensive NULL assignment to protect against a
not-too-smart compiler warning about unitialized variable use after the
switch. Unfortunately I only did so on master and forgot to adjust that for
14.

Stephen noticed that there actually is a compiler warning :(.

Reported-By: Stephen Frost <sfrost@snowman.net>
Discussion: https://postgr.es/m/20210827224639.GX17906@tamriel.snowman.net

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0d0bbee5e3ee2eabe3a1f6081cbc4226520764c0

Modified Files
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src/backend/storage/ipc/procarray.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)