pgsql: Fix oversight from 9e149c8 with spin-lock handling

Fix oversight from 9e149c8 with spin-lock handling

Calling an external function while a pin-lock is held is a bad idea as
those are designed to be short-lived.  The stress of a first commit into
a large git history may contribute to that.

Reported-by: Andres Freund
Discussion: https://postgr.es/m/20180611164952.vmxdpdpirdtkdsz6@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f8795d2ec8632a7242896e0f8322d13bfe922512

Modified Files
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src/backend/replication/slot.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)