fix(MdListItem): reduce function complexity (#1853)

Author: ldursw

src/components/MdList/MdListItem/MdListItem.vue

@@ -67,15 +67,19 @@
     }
 
     if (shouldRenderButtonWithListener(listeners)) {
-      if (hasChildrenButtons(children)) {
-        return MdListItemFakeButton
-      }
-      return MdListItemButton
+      return renderButtonWithListener(children)
     }
 
     return MdListItemDefault
   }
 
+  function renderButtonWithListener (children) {
+    if (hasChildrenButtons(children)) {
+      return MdListItemFakeButton
+    }
+    return MdListItemButton
+  }
+
   export default {
     name: 'MdListItem',
     functional: true,