ability to slice an undefined pointer at compile time if the len is 0

src/codegen.cpp

@@ -4201,6 +4201,7 @@ static LLVMValueRef gen_const_val(CodeGen *g, ConstExprValue *const_val, const c
                             continue;
                         }
                         ConstExprValue *field_val = &const_val->data.x_struct.fields[i];
+                        assert(field_val->type != nullptr);
                         LLVMValueRef val = gen_const_val(g, field_val, "");
                         fields[type_struct_field->gen_index] = val;
                         make_unnamed_struct = make_unnamed_struct || is_llvm_value_unnamed_type(field_val->type, val);