Fix DefaultHttpDataSource read when requested length is 0

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134063990

library/src/main/java/com/google/android/exoplayer2/upstream/DefaultHttpDataSource.java

@@ -547,11 +547,8 @@ public class DefaultHttpDataSource implements HttpDataSource {
    * @throws IOException If an error occurs reading from the source.
    */
   private int readInternal(byte[] buffer, int offset, int readLength) throws IOException {
-    readLength = bytesToRead == C.LENGTH_UNSET ? readLength
-        : (int) Math.min(readLength, bytesToRead - bytesRead);
     if (readLength == 0) {
-      // We've read all of the requested data.
-      return C.RESULT_END_OF_INPUT;
+      return 0;
     }
 
     int read = inputStream.read(buffer, offset, readLength);