Update DataReader.java

make rewind() method fully rewind the stream

app/src/main/java/org/schabi/newpipe/streams/DataReader.java

@@ -137,6 +137,7 @@ public class DataReader {
 
         position = 0;
         readOffset = readBuffer.length;
+        readCount = 0;
     }
 
     public boolean canRewind() {