Description:
------------
pg_fetch_array(), pg_fetch_assoc(), pg_fetch_object() and pg_fetch_row() neglect to raise a warning when requesting $row = -1. In some cases, -1 is interpreted as though $row = NULL.

pg_fetch_result() is not affected.

Test script:
---------------
<?php
error_reporting(E_ALL);
$conn = pg_connect('host=localhost dbname=postgres');

$result = pg_query("select 'a' union select 'b'");
var_dump(pg_fetch_row($result, -1));
var_dump(pg_fetch_row($result, -1));

$result = pg_query("select 'a' union select 'b'");
var_dump(pg_fetch_row($result, -2));
var_dump(pg_fetch_row($result, -1));
var_dump(pg_fetch_row($result, -1));

$result = pg_query("select 'a' union select 'b'");
var_dump(pg_fetch_row($result, 0));
var_dump(pg_fetch_row($result, -1));
var_dump(pg_fetch_row($result, -1));

Expected result:
----------------
PHP Warning:  pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 5 in pgsql_bug.php on line 6

Warning: pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 5 in pgsql_bug.php on line 6
bool(false)
PHP Warning:  pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 5 in pgsql_bug.php on line 7

Warning: pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 5 in pgsql_bug.php on line 7
bool(false)
PHP Warning:  pg_fetch_row(): Unable to jump to row -2 on PostgreSQL result index 6 in pgsql_bug.php on line 10

Warning: pg_fetch_row(): Unable to jump to row -2 on PostgreSQL result index 6 in pgsql_bug.php on line 10
bool(false)
PHP Warning:  pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 6 in pgsql_bug.php on line 11

Warning: pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 6 in pgsql_bug.php on line 11
bool(false)
PHP Warning:  pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 6 in pgsql_bug.php on line 12

Warning: pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 6 in pgsql_bug.php on line 12
bool(false)
array(1) {
  [0]=>
  string(1) "a"
}
PHP Warning:  pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 7 in pgsql_bug.php on line 16

Warning: pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 7 in pgsql_bug.php on line 16
bool(false)
PHP Warning:  pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 7 in pgsql_bug.php on line 17

Warning: pg_fetch_row(): Unable to jump to row -1 on PostgreSQL result index 7 in pgsql_bug.php on line 17
bool(false)

Actual result:
--------------
array(1) {
  [0]=>
  string(1) "a"
}
array(1) {
  [0]=>
  string(1) "b"
}
PHP Warning:  pg_fetch_row(): Unable to jump to row -2 on PostgreSQL result index 6 in pgsql_bug.php on line 10

Warning: pg_fetch_row(): Unable to jump to row -2 on PostgreSQL result index 6 in pgsql_bug.php on line 10
bool(false)
bool(false)
bool(false)
array(1) {
  [0]=>
  string(1) "a"
}
array(1) {
  [0]=>
  string(1) "a"
}
array(1) {
  [0]=>
  string(1) "b"
}