Be tolerant of theaters with no airfield data.

This shouldn't be the case for anything shipped, but is typical when new
theaters are still being developed.

We could potentially add an `in_progress` flag to the theater definition
to make this only optionally tolerant, but since that code path would
rarely be exercised it's just likely to bitrot. This data isn't critical
to mission generation anyway, so this is fine. What we should do is add
some linters that document all the data that is missing though (and
ideally publish that to our docs).

game/airfields.py

@@ -5,14 +5,15 @@ data added to pydcs. Until then, missing data can be manually filled in here.
 """
 from __future__ import annotations
 
+import logging
 from collections.abc import Iterator
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Any, ClassVar, Dict, Optional, TYPE_CHECKING, Tuple
 
 import yaml
-from dcs.terrain import Airport
 from dcs.task import Modulation
+from dcs.terrain import Airport
 
 from game.radio.radios import RadioFrequency
 from game.radio.tacan import TacanChannel
@@ -168,9 +169,12 @@ class AirfieldData:
 
         airfields = {}
         base_path = Path("resources/airfields") / theater.terrain.name
+        if base_path.is_dir():
             for airfield_yaml in base_path.iterdir():
                 data = cls.from_file(airfield_yaml)
                 airfields[data.id] = data
+        else:
+            logging.warning("No airfield data available for %s", theater.terrain.name)
         cls._airfields[theater.terrain.name] = airfields
 
     @classmethod