ensure first_log doesn't change on append

test/append-test-log.c

@@ -96,6 +96,15 @@ append_to_existing(TestState *s)
 	test.last_log = &second;
 
 	append_test_log(&test, "baz");
+
+	// first shouldn't change
+	print("\t\tfirst_log\n");
+	chk_ptr_eq(
+		s,
+		"ERROR: append_test_log(): first_log:",
+		test.first_log,
+		&first
+	);
 }
 
 //jl