PARQUET-787: Update tests for both ByteBufferInputStreams.

Author: rdblue

parquet-common/src/main/java/org/apache/parquet/bytes/MultiBufferInputStream.java

@@ -155,6 +155,7 @@ public ByteBuffer slice(int length) throws EOFException {
       slice = current.duplicate();
       slice.limit(slice.position() + length);
       current.position(slice.position() + length);
+      this.position += length;
     }
 
     return slice;

parquet-common/src/main/java/org/apache/parquet/bytes/SingleBufferInputStream.java

@@ -126,6 +126,10 @@ public ByteBuffer slice(int length) throws EOFException {
 
   @Override
   public List<ByteBuffer> sliceBuffers(long length) throws EOFException {
+    if (length == 0) {
+      return Collections.emptyList();
+    }
+
     if (length > buffer.remaining()) {
       throw new EOFException();
     }