fix: Add a null check in ILPP to handle unresolvable types. (#2485)

Author: ShadauxCat

com.unity.netcode.gameobjects/Editor/CodeGen/NetworkBehaviourILPP.cs

@@ -840,7 +840,7 @@ private void GetAllFieldsAndResolveGenerics(TypeDefinition type, ref List<TypeRe
         private void GetAllBaseTypesAndResolveGenerics(TypeDefinition type, ref List<TypeReference> baseTypes, Dictionary<string, TypeReference> genericParameters)
         {
 
-            if (type.BaseType == null || type.BaseType.Name == "Object")
+            if (type == null || type.BaseType == null || type.BaseType.Name == "Object")
             {
                 return;
             }