fix /envpreset save no longer working if there was a general error reading envpresets.txt

Author: UnknownShadow200

fCraft/World/EnvPresets.cs

@@ -164,7 +164,7 @@ public static void LoadAll() {
                 }
                 Logger.Log(LogType.SystemActivity, "EnvPresets.Load: Loaded " + count + " presets");
             } catch (Exception ex) {
-                Presets = null;
+                Presets = new List<EnvPresets>();
                 Logger.Log(LogType.Error, "EnvPresets.Load: " + ex);
             }
         }