Check for valid columns in adodb postgres64 driver MetaIndexes fn (bug #796102)

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.

Change-Id: I1464b8a9fda8bd137dcabf1145da289ccf32c500
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>

htdocs/lib/adodb/README.mahara

@@ -9,3 +9,5 @@ Modifications:
 - drivers/adodb-mysql.inc.php (24465d23e2ccb3a89629e250a3caab1ee051e90d)
 - drivers/adodb-postgres7.inc.php (af59ab96086a319785ed682420d22dbfcbacb9bc)
 - adodb/drivers/adodb-postgres64.inc.php (d6d8884fabc598aec58e633a6a1e258cd07b3da1)
+- Add check for valid columns in MetaIndexes function of
+  adodb/drivers/adodb-postgres64.inc.php (see bug #796102)

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

@@ -633,7 +633,9 @@ WHERE (c2.relname=\'%s\' or c2.relname=lower(\'%s\'))';
                 while ($row = $rs->FetchRow()) {
                         $columns = array();
                         foreach (explode(' ', $row[2]) as $col) {
+                            if (isset($col_names[$col])) {
                                 $columns[] = $col_names[$col];
+                            }
                         }
                         
                         $indexes[$row[0]] = array(