Javadoc: Add missing constructor Javadoc comments

Author: garydgregory

src/main/java/org/apache/commons/io/output/AbstractByteArrayOutputStream.java

@@ -98,6 +98,13 @@ protected interface InputStreamConstructor<T extends InputStream> {
     /** Flag to indicate if the buffers can be reused after reset */
     private boolean reuseBuffers = true;
 
+    /**
+     * Constructs a new instance for subclasses.
+     */
+    public AbstractByteArrayOutputStream() {
+        // empty
+    }
+
     /**
      * Does nothing.
      *