Fix issue with zero arg @operator(construct). Assert on add to uninitialized ct variable #1765

test/test_suite/compile_time/add_to_ct_undefined.c3

@@ -0,0 +1,6 @@
+fn int main()
+{
+	var $a;
+	$a += 1; // #error: not yet initialized
+	return 0;
+}

test/test_suite/overloading/construct_op_zero_args.c3

@@ -0,0 +1,5 @@
+struct Foo { int a; }
+fn Foo Foo.foo() @operator(construct)
+{
+	return { 1 };
+}