title: Query return empty when Left Join table is empty in codeigniter
body: <p>I'm using Codeigniter with MySql 7.5. I have a query and it always returns empty when left join table is empty.</p>
  
  <pre><code>$this-&gt;db-&gt;select('shop.id as shop_id, shop.shop_name, rg.rating');
  $this-&gt;db-&gt;from('shop');            
  $this-&gt;db-&gt;join('booking as bh', 'bh.shop_id = shop.id', 'left');
  $this-&gt;db-&gt;join('rating rg', 'rg.booking_id = bh.id', 'left');
  $this-&gt;db-&gt;group_by("bh.id");
  $this-&gt;db-&gt;order_by("bh.id", "desc");
  </code></pre>
  
  <p>Here I have entries in booking and shop tables but rating table is empty. But I didn't get any results.</p>
  
  <p>If I remove <code>rg.rating</code> from select it will return correct result.</p>
  
  <p>Did I miss anything? Thanks</p>