fix renderer parameter in older django versions

Author: manelclos

smart_selects/widgets.py

@@ -150,7 +150,10 @@ def render(self, name, value, attrs=None, choices=(), renderer=None):  # noqa: C
         else:
             final_attrs['class'] = 'chained-fk'
 
-        output = super(ChainedSelect, self).render(name, value, final_attrs, renderer)
+        if renderer:
+            output = super(ChainedSelect, self).render(name, value, final_attrs, renderer)
+        else:
+            output = super(ChainedSelect, self).render(name, value, final_attrs)
 
         return mark_safe(output)
 
@@ -262,6 +265,9 @@ def render(self, name, value, attrs=None, choices=(), renderer=None):
             # For hozontal mode add django filter horizontal javascript selector class
             final_attrs['class'] += ' selectfilter'
         final_attrs['data-field-name'] = self.verbose_name
-        output = super(ChainedSelectMultiple, self).render(name, value, final_attrs, renderer)
+        if renderer:
+            output = super(ChainedSelectMultiple, self).render(name, value, final_attrs, renderer)
+        else:
+            output = super(ChainedSelectMultiple, self).render(name, value, final_attrs)
 
         return mark_safe(output)