Fix bug for file with invalid-utf8 filenames

tests/examples/test-invalid-utf8-�(.rs

@@ -0,0 +1,4 @@
+fn print_square(num: f64) {
+    let result = f64::powf(num, 2.0);
+    println!("The square of {:.2} is {:.2}.", num, result);
+}