fix(MpegTrackFragmentHeader): Use sampleSizes if present

Fix discovered by @viztea

Author: devoxin

main/src/main/java/com/sedmelluq/discord/lavaplayer/container/mpeg/reader/fragmented/MpegTrackFragmentHeader.java

@@ -127,7 +127,7 @@ public void setSize(int i, int value) {
         public MpegTrackFragmentHeader build() {
             int[] finalSampleSizes = sampleSizes;
 
-            if (defaultSampleSize != 0) {
+            if (finalSampleSizes == null && defaultSampleSize != 0) {
                 finalSampleSizes = new int[sampleCount];
 
                 for (int i = 0; i < sampleCount; i++) {