Fix #4892 - update_batch()

Regression caused by 0c23e9122666a30797079bea9415da135d4f7e12 trying to fix #4871

Supersedes #4929
diff --git a/system/database/drivers/postgre/postgre_driver.php b/system/database/drivers/postgre/postgre_driver.php
index dfd87f9..51916fc 100644
--- a/system/database/drivers/postgre/postgre_driver.php
+++ b/system/database/drivers/postgre/postgre_driver.php
@@ -550,13 +550,13 @@
 		$ids = array();
 		foreach ($values as $key => $val)
 		{
-			$ids[] = $val[$index];
+			$ids[] = $val[$index]['value'];
 
 			foreach (array_keys($val) as $field)
 			{
 				if ($field !== $index)
 				{
-					$final[$field][] = 'WHEN '.$val[$index].' THEN '.$val[$field];
+					$final[$val[$field]['field']][] = 'WHEN '.$val[$index]['value'].' THEN '.$val[$field]['value'];
 				}
 			}
 		}
@@ -564,12 +564,12 @@
 		$cases = '';
 		foreach ($final as $k => $v)
 		{
-			$cases .= $k.' = (CASE '.$index."\n"
+			$cases .= $k.' = (CASE '.$val[$index]['field']."\n"
 				.implode("\n", $v)."\n"
 				.'ELSE '.$k.' END), ';
 		}
 
-		$this->where($index.' IN('.implode(',', $ids).')', NULL, FALSE);
+		$this->where($val[$index]['field'].' IN('.implode(',', $ids).')', NULL, FALSE);
 
 		return 'UPDATE '.$table.' SET '.substr($cases, 0, -2).$this->_compile_wh('qb_where');
 	}