pgsql: Fix an issue in PostgreSQL::Test::Cluster:psql()

Fix an issue in PostgreSQL::Test::Cluster:psql()

Due to the commit c5385929 which made all Perl warnings to fatal, use
of PostgreSQL::Test::Cluster:psql() and safe_psql() with timeout
started to fail with the following error:

Use of uninitialized value $ret in bitwise and (&) at
..src/test/perl/PostgreSQL/Test/Cluster.pm line 2015.

Fix that by placing $ret conversion code in psql() in an if (defined
$ret) block.

With this change, the behavior of psql() becomes same as before, that
is, the whole function returns undef on timeout, which is usefully
different from returning 0.

Author: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/06f899fd-1826-05ab-42d6-adeb1fd5e200%40eisentraut.org

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/686db12de3a01222de6bce56f40f4fb9259f7b37

Modified Files
--------------
src/test/perl/PostgreSQL/Test/Cluster.pm | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)