Add regression tests from fuzzing test cases.

This is the test case from frewsxcv's fuzzing work,
generated by American Fuzzy Lop's rust support.

#2

tests/afl.rs

@@ -0,0 +1,17 @@
+// Regression tests from American Fuzzy Lop test cases.
+
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+extern crate mp4parse;
+
+use std::io::Cursor;
+
+/// https://github.com/mozilla/mp4parse-rust/issues/2
+#[test]
+fn fuzz_2() {
+    let mut c = Cursor::new(b"\x00\x00\x00\x04\xa6\x00\x04\xa6".to_vec());
+    let mut context = mp4parse::MediaContext::new();
+    let _ = mp4parse::read_box(&mut c, &mut context);
+}