throw ArithmeticException on integer overflow from size

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>

jetty-io/src/main/java/org/eclipse/jetty/io/ByteBufferAccumulator.java

@@ -59,7 +59,7 @@ public class ByteBufferAccumulator implements AutoCloseable
     {
         int length = 0;
         for (ByteBuffer buffer : _buffers)
-            length += buffer.remaining();
+            length = Math.addExact(length, buffer.remaining());
         return length;
     }