Ignore parse errors in Liberation prefs.

Before this patch, if this file is corrupt (or the format changes in a
way pydcs doesn't expect), pydcs will crash on import since the livery
scanner runs at import time.

dcs/liveries_scanner.py

@@ -26,17 +26,28 @@ def regex_group_extractor(regex: str, text: str, fallback=None):
 
 
 def read_liberation_preferences() -> Tuple[str, str]:
+    # TODO: Remove Liberation-specific behavior.
+    # This is only necessary because it doesn't appear to be possible to 100% reliably
+    # guess the DCS install or user directory. Liberation solves this by just asking the
+    # user on first run. That's a problem for every pydcs user, not just Liberation.
+    # This should go away in favor of making dcs.installation *guess* at the paths, but
+    # with an API to override from the app side (similar to PayloadDirectories APIs).
     install = ""
     saved_games = ""
     pref_path = os.path.join(os.path.expanduser("~"), "AppData", "Local", "DCSLiberation")
     pref_path = os.path.join(pref_path, "liberation_preferences.json")
     if os.path.exists(pref_path):
         with open(pref_path, "r") as file:
-            json_dict = json.load(file)
-            if "dcs_install_dir" in json_dict:
-                install = json_dict["dcs_install_dir"]
-            if "saved_game_dir" in json_dict:
-                saved_games = json_dict["saved_game_dir"]
+            try:
+                json_dict = json.load(file)
+                if "dcs_install_dir" in json_dict:
+                    install = json_dict["dcs_install_dir"]
+                if "saved_game_dir" in json_dict:
+                    saved_games = json_dict["saved_game_dir"]
+            except (KeyError, ValueError):
+                # ValueError for decode errors (if the file is corrupted), KeyError in
+                # case the format isn't what we expect.
+                return "", ""
     return install, saved_games