Don't fail on empty audio blocks

Summary:
When the provided sample count is zero, it means it's not explicitly provided and we may need to compute it according to the content block's size. This diff makes sure, that:
- we send a onAudioRead notification is sent in all cases
- we use the form that explicitly sets the size of the block, if we can't compute the sample's count based on the remaining size.

Reviewed By: kiminoue7

Differential Revision: D52225600

fbshipit-source-id: 9dbc0af8c242b1e3828959787e7052579d1315b2

vrs/ContentBlockReader.cpp

@@ -144,7 +144,7 @@ bool AudioBlockReader::readAudioContentBlock(
   size_t sampleCount = audioContent.getSampleCount();
   if (sampleCount == 0) {
     if (remainingBlockSize != ContentBlock::kSizeUnknown) {
-      if (audioContent.getAudioFormat() == AudioFormat::PCM) {
+      if (remainingBlockSize > 0 && audioContent.getAudioFormat() == AudioFormat::PCM) {
         // The sample count is undefined, but we can to do the math,
         // using the remaining bytes in the record.
         uint8_t sampleBlockStride = audioContent.getSampleBlockStride();
@@ -160,10 +160,9 @@ bool AudioBlockReader::readAudioContentBlock(
                   static_cast<uint32_t>(remainingBlockSize / sampleBlockStride),
                   audioContent.getSampleBlockStride()));
         }
-      } else {
-        return player.onAudioRead(
-            record, blockIndex_, ContentBlock(contentBlock, remainingBlockSize));
       }
+      return player.onAudioRead(
+          record, blockIndex_, ContentBlock(contentBlock, remainingBlockSize));
     }
   } else {
     size_t expectedSize = sampleCount * audioContent.getSampleBlockStride();