Include airport countries in trip country list

agenda/types.py

@@ -159,6 +159,19 @@ class Trip:
             assert country
             items.append(country)
 
+        for item in self.travel:
+            if item["type"] != "flight":
+                continue
+
+            for key in "from_airport", "to_airport":
+                c = item[key]["country"]
+                if c in seen:
+                    continue
+                seen.add(c)
+                country = agenda.get_country(c)
+                assert country
+                items.append(country)
+
         return items
 
     @property