Update DB_query_builder.php

recent changes broke query ordering giving a warning in line 1238 = '$this->qb_cache_orderby = array_merge($this->qb_cache_orderby, $qb_orderby);'
this was because on subsequent re-queries, the qb_cache_orderby was set to NULL not Array() as it is should be (and is instantiated originally .

system/database/DB_query_builder.php

@@ -1405,7 +1405,7 @@ public function count_all_results($table = '', $reset = TRUE)
 		// for selecting COUNT(*) ...
 		$qb_orderby       = $this->qb_orderby;
 		$qb_cache_orderby = $this->qb_cache_orderby;
-		$this->qb_orderby = $this->qb_cache_orderby = NULL;
+		$this->qb_orderby = $this->qb_cache_orderby = array();
 
 		$result = ($this->qb_distinct === TRUE OR ! empty($this->qb_groupby) OR ! empty($this->qb_cache_groupby) OR $this->qb_limit OR $this->qb_offset)
 			? $this->query($this->_count_string.$this->protect_identifiers('numrows')."\nFROM (\n".$this->_compile_select()."\n) CI_count_all_results")