Fix avif_fuzztest_enc_dec_anim for AVIF_ADD_IMAGE_FLAG_SINGLE (AOMedi…

…aCodec#1940)

BUG=oss-fuzz:65696

tests/gtest/avif_fuzztest_enc_dec_anim.cc

@@ -35,10 +35,26 @@ void EncodeDecodeAnimation(ImagePtr frame,
   int total_duration = 0;
 
   // Encode.
-  for (const FrameOptions& options : frame_options) {
+  for (size_t i = 0; i < frame_options.size(); ++i) {
+    const FrameOptions& options = frame_options[i];
     total_duration += options.duration;
     const avifResult result = avifEncoderAddImage(
         encoder.get(), frame.get(), options.duration, options.flags);
+    // AVIF_ADD_IMAGE_FLAG_SINGLE can only be used on one image.
+    if ((frame_options[0].flags & AVIF_ADD_IMAGE_FLAG_SINGLE) && i > 0) {
+      ASSERT_EQ(result, AVIF_RESULT_ENCODE_COLOR_FAILED)
+          << avifResultToString(result) << " " << encoder->diag.error;
+      return;
+    }
+    // AVIF_ADD_IMAGE_FLAG_SINGLE can only be used on the first image.
+    // It also cannot be set for layered images.
+    if ((options.flags & AVIF_ADD_IMAGE_FLAG_SINGLE) &&
+        (i > 0 || encoder->extraLayerCount > 0)) {
+      ASSERT_EQ(result, AVIF_RESULT_INVALID_ARGUMENT)
+          << avifResultToString(result) << " " << encoder->diag.error;
+      return;
+    }
+
     ASSERT_EQ(result, AVIF_RESULT_OK)
         << avifResultToString(result) << " " << encoder->diag.error;
   }