mp4-remuxer: don't filter audio frame with pts=0

fix livestream playback issues on  OS X 10.12 and less

src/remux/mp4-remuxer.js

@@ -467,7 +467,7 @@ class MP4Remuxer {
     // if we don't remove these negative samples, they will shift all audio samples forward.
     // leading to audio overlap between current / next fragment
     inputSamples = inputSamples.filter(function(sample) {
-      return sample.pts > 0;
+      return sample.pts >= 0;
     });
 
     // in case all samples have negative PTS, and have been filtered out, return now