FragmentedMp4Extractor: allow both first_sample_flags and sample_flags

Having both in the trun box is not allowed (see section section 8.8.8.1
of ISO/IEC 14496-12:2015) but this CL makes the code more robust in case
this happens. Before this change, the first sample flag was not read,
making subsequent reads incorrect.

Issue: #7698
PiperOrigin-RevId: 325212160

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java

@@ -997,8 +997,10 @@ private static int parseTrun(
           checkNonNegative(sampleDurationsPresent ? trun.readInt() : defaultSampleValues.duration);
       int sampleSize =
           checkNonNegative(sampleSizesPresent ? trun.readInt() : defaultSampleValues.size);
-      int sampleFlags = (i == 0 && firstSampleFlagsPresent) ? firstSampleFlags
-          : sampleFlagsPresent ? trun.readInt() : defaultSampleValues.flags;
+      int sampleFlags =
+          sampleFlagsPresent
+              ? trun.readInt()
+              : (i == 0 && firstSampleFlagsPresent) ? firstSampleFlags : defaultSampleValues.flags;
       if (sampleCompositionTimeOffsetsPresent) {
         // The BMFF spec (ISO 14496-12) states that sample offsets should be unsigned integers in
         // version 0 trun boxes, however a significant number of streams violate the spec and use