CONTRIB-2970 header printed too early

Credit goes to Sam Chaffee.

view.php

@@ -125,8 +125,6 @@ $PAGE->set_heading(format_string($course->fullname));
 
 book_add_fake_block($chapters, $chapter, $book, $cm, $edit);
 
-echo $OUTPUT->header();
-
 /// prepare chapter navigation icons
 $previd = null;
 $nextid = null;
@@ -169,6 +167,8 @@ if ($nextid) {
 // Book display HTML code
 // =====================================================
 
+echo $OUTPUT->header();
+
 // upper nav
 echo '<div class="navtop">'.$chnavigation.'</div>';