Fixed double check idiom example from page 334 as was done in the thi…

…rd printing.

See errata page for details:
    https://docs.google.com/document/d/1mAeEgQu4H4ADxa03k7YaVDjIP5vJBvjVIjg3DIvoc8E/

src/effectivejava/chapter11/item83/Initialization.java

@@ -25,6 +25,7 @@ private static class FieldHolder {
     // Double-check idiom for lazy initialization of instance fields - Page 334
     private volatile FieldType field4;
 
+    // NOTE: The code for this method in the first printing had a serious error (see errata for details)!
     private FieldType getField4() {
         FieldType result = field4;
         if (result != null)    // First check (no locking)
@@ -38,6 +39,7 @@ private FieldType getField4() {
     }
 
 
+
     // Single-check idiom - can cause repeated initialization! - Page 334
     private volatile FieldType field5;