Relax SampleTransformZeroInputItemsRejected error

In the SampleTransformZeroInputItemsRejected test, do not require the
error code of avifDecoderReadMemory() be AVIF_RESULT_BMFF_PARSE_FAILED.
This allows the implementation to return a different error code such as
AVIF_RESULT_DECODE_SAMPLE_TRANSFORM_FAILED.

Note: Without this change, the next statement,
  EXPECT_NE(result, AVIF_RESULT_INTERNAL_ERROR);
is redundant.

tests/gtest/avifaltrtest.cc

diff --git a/tests/gtest/avifaltrtest.cc b/tests/gtest/avifaltrtest.cc
index f8b4c72..28a0822 100644
--- a/tests/gtest/avifaltrtest.cc
+++ b/tests/gtest/avifaltrtest.cc
@@ -140,7 +140,7 @@
   ASSERT_NE(image, nullptr);
   const avifResult result = avifDecoderReadMemory(decoder.get(), image.get(),
                                                   encoded.data, encoded.size);
-  EXPECT_EQ(result, AVIF_RESULT_BMFF_PARSE_FAILED);
+  EXPECT_NE(result, AVIF_RESULT_OK);
   EXPECT_NE(result, AVIF_RESULT_INTERNAL_ERROR);
 }