Add support for unknown errors (#251)

## Description

-   Handle unknown errors in the avatarLoader.

Author: rk132

Runtime/Core/Scripts/AvatarObjectLoader.cs

@@ -144,6 +144,11 @@ private async void Load(string url)
                 Failed(executor.IsCancelled ? FailureType.OperationCancelled : exception.FailureType, exception.Message);
                 return;
             }
+            catch (Exception e)
+            {
+                Failed(FailureType.Unknown, e.Message);
+                return;
+            }
 
             var avatar = (GameObject) context.Data;
             avatar.SetActive(true);

Runtime/Core/Scripts/Data/Enums.cs

@@ -98,7 +98,8 @@ public enum FailureType
         DirectoryAccessError,
         AvatarProcessError,
         AvatarRenderError,
-        OperationCancelled
+        OperationCancelled,
+        Unknown
     }
 
     public enum Expression