readHeader() can be final

Author: thurka

visualvm/libs.profiler/lib.profiler/src/org/graalvm/visualvm/lib/jfluid/heap/HprofByteBuffer.java

@@ -131,7 +131,7 @@ long capacity() {
 
     abstract void get(long position, byte[] chars);
 
-    void readHeader() throws IOException {
+    final void readHeader() throws IOException {
         long[] offset = new long[1];
         String magic = readStringNull(offset, MINIMAL_SIZE);