title: add else conditional to simplified structure block
body: <p>Good morning,
  I have an if for code to which I want to add an else statement, but it is giving me an error.
  How could I do it.
  Thanks a lot.</p>
  
  <p>code to which I want to add the: <code>if line_tax.price_include</code>
  equivalent to code (b)</p>
  
  <pre><code>self.total_des = sum([
       line.price_unit2*line.quantity for line in self.invoice_line_ids 
       if len([line.price_unit2*line.quantity for line_tax in line.invoice_line_tax_ids if line_tax.tipo.code in ["A"]] )
  ])
  </code></pre>
  
  <p>code (b):</p>
  
  <pre><code>self.total_des=0
  for line in self.invoice_line_ids:
      for line_tax in line.invoice_line_tax_ids:
          if line_tax.tipo in ["A"]:
              if line_tax.price_include: 
                  self.total_des=self.total_des+line.price_unit2*line.quantity
              else:
                  self.total_des=self.total_des+line.price_unit2*line.quantity*-1
  </code></pre>