Check for valid columns in adodb postgres64 driver MetaIndexes fn

Bug 1384473

Indexes on functions of columns have a 0 in the indkey column of
pg_catalog.pg_index, which doesn't refer to a column.

Don't return any columns for the index, rather than returning an empty
column name.

(cherry picked from commit b87d9961)

Change-Id: Idd9bcdd04f15c99e76e028d62236a4d932ee845c
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>

htdocs/lib/adodb/drivers/adodb-postgres64.inc.php

@@ -651,7 +651,9 @@ a different OID if a database must be reloaded. */
 		while ($row = $rs->FetchRow()) {
 			$columns = array();
 			foreach (explode(' ', $row[2]) as $col) {
-				$columns[] = $col_names[$col];
+                if (isset($col_names[$col])) {
+                    $columns[] = $col_names[$col];
+                }
 			}
 
 			$indexes[$row[0]] = array(