[JASSIST-131] Fix ConstPoolWriter.addStringInfo()

git-svn-id: http://anonsvn.jboss.org/repos/javassist/trunk@570 30ef5769-5b8d-40dd-aea6-55b5d6557bb3

src/main/javassist/bytecode/ClassFileWriter.java

          * @return          the index of the added entry.
          */
         public int addStringInfo(String str) {
+            int utf8 = addUtf8Info(str);
             output.write(StringInfo.tag);
-            output.writeShort(addUtf8Info(str));
+            output.writeShort(utf8);
             return num++;
         }