Fix data_offset not present bug in FragmentedMp4Extractor

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=131183033

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

@@ -664,8 +664,9 @@ public final class FragmentedMp4Extractor implements Extractor {
     DefaultSampleValues defaultSampleValues = fragment.header;
     DefaultSampleValues defaultSampleValues = fragment.header;
 
 
     fragment.trunLength[index] = trun.readUnsignedIntToInt();
     fragment.trunLength[index] = trun.readUnsignedIntToInt();
+    fragment.trunDataPosition[index] = fragment.dataPosition;
     if ((atomFlags & 0x01 /* data_offset_present */) != 0) {
     if ((atomFlags & 0x01 /* data_offset_present */) != 0) {
-      fragment.trunDataPosition[index] = fragment.dataPosition + trun.readInt();
+      fragment.trunDataPosition[index] += trun.readInt();
     }
     }
 
 
     boolean firstSampleFlagsPresent = (atomFlags & 0x04 /* first_sample_flags_present */) != 0;
     boolean firstSampleFlagsPresent = (atomFlags & 0x04 /* first_sample_flags_present */) != 0;