pgsql: pg_controldata: Prevent division-by-zero errors

pg_controldata: Prevent division-by-zero errors

If the control file is corrupted and specifies the WAL segment size
to be 0 bytes, calculating the latest checkpoint's REDO WAL file
will fail with a division-by-zero error. Show it as "???" instead.

Also reword the warning message a bit and send it to stdout, like the
other pre-existing warning messages.

Add some tests for dealing with a corrupted pg_control file.

Author: Nathan Bossart <bossartn(at)amazon(dot)com>, tests by me

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4731d848f23e08a9396b4831d13fbb6dd460faf2

Modified Files
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src/bin/pg_controldata/pg_controldata.c | 26 ++++++++++++++++++--------
src/bin/pg_controldata/t/001_pg_controldata.pl | 21 ++++++++++++++++++++-
2 files changed, 38 insertions(+), 9 deletions(-)