pgsql: Reduce code duplication between heapgettup and heapgettup_pagemo

Reduce code duplication between heapgettup and heapgettup_pagemode

The code to get the next block number was exactly the same between these
two functions, so let's just put it into a helper function and call that
from both locations.

Author: Melanie Plageman
Reviewed-by: Andres Freund, David Rowley
Discussion: https://postgr.es/m/CAAKRu_bvkhka0CZQun28KTqhuUh5ZqY=_T8QEqZqOL02rpi2bw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7ae0ab0ad9704b10400a611a9af56c63304c27a5

Modified Files
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src/backend/access/heap/heapam.c | 186 +++++++++++++++++++--------------------
1 file changed, 91 insertions(+), 95 deletions(-)