Add a decoder test that parses empty data

Add a test for the following pull requests:
https://github.com/AOMediaCodec/libavif/pull/1768
https://github.com/AOMediaCodec/libavif/pull/1779

tests/gtest/avifdecodetest.cc

diff --git a/tests/gtest/avifdecodetest.cc b/tests/gtest/avifdecodetest.cc
index 285d9d3..10e66a0 100644
--- a/tests/gtest/avifdecodetest.cc
+++ b/tests/gtest/avifdecodetest.cc
@@ -1,6 +1,9 @@
 // Copyright 2023 Google LLC
 // SPDX-License-Identifier: BSD-2-Clause
 
+#include <iostream>
+#include <string>
+
 #include "avif/avif.h"
 #include "aviftest_helpers.h"
 #include "gtest/gtest.h"
@@ -30,6 +33,14 @@
   EXPECT_GT(decoder->image->alphaRowBytes, 0u);
 }
 
+TEST(AvifDecodeTest, ParseEmptyData) {
+  DecoderPtr decoder(avifDecoderCreate());
+  ASSERT_NE(decoder, nullptr);
+  ASSERT_EQ(avifDecoderSetIOMemory(decoder.get(), nullptr, 0), AVIF_RESULT_OK);
+  // No ftyp box was seen.
+  ASSERT_EQ(avifDecoderParse(decoder.get()), AVIF_RESULT_INVALID_FTYP);
+}
+
 }  // namespace
 }  // namespace avif