Make sure to run one initdb TAP test with no TZ set

That way we make sure that initdb's time zone setting code is exercised.
This doesn't add an extra test, it just alters an existing test.

Discussion: <https://postgr.es/m/5807.1492229253@sss.pgh.pa.us>

src/bin/initdb/t/001_initdb.pl

@@ -34,8 +34,16 @@ command_fails(
 	'role names cannot begin with "pg_"');
 
 mkdir $datadir;
-command_ok([ 'initdb', '-N', '-T', 'german', '-X', $xlogdir, $datadir ],
-	'successful creation');
 
+# make sure we run one successful test without a TZ setting so we test
+# initdb's time zone setting code
+{
+	# delete local only works from perl 5.12, so use the older way to do this
+	local (%ENV) = %ENV;
+	delete $ENV{TZ};
+
+	command_ok([ 'initdb', '-N', '-T', 'german', '-X', $xlogdir, $datadir ],
+		'successful creation');
+}
 command_ok([ 'initdb', '-S', $datadir ], 'sync only');
 command_fails([ 'initdb', $datadir ], 'existing data directory');