MDL-67524 book: fixing view hidden chapter issue

* Users who has permission should be able to view after turning editing off

mod/book/tests/behat/show_hide_chapters.feature

@@ -58,11 +58,6 @@ Feature: Book activity chapter visibility management
     And I follow "Test book"
     Then the "class" attribute of "a[title='Second chapter']" "css_element" should contain "dimmed_text"
     And the "class" attribute of "a[title='Third chapter']" "css_element" should contain "dimmed_text"
-    And I follow "Next"
-    And I should see "Fourth chapter" in the ".book_content" "css_element"
-    And I follow "Exit book"
-    And I follow "Test book"
-    And I should see "First chapter" in the ".book_content" "css_element"
     And I turn editing mode on
     And I follow "Next"
     And I should see "Second chapter" in the ".book_content" "css_element"
@@ -80,3 +75,8 @@ Feature: Book activity chapter visibility management
     And I follow "Test book"
     And I should not see "Second chapter" in the "Table of contents" "block"
     And I should not see "Third chapter" in the "Table of contents" "block"
+    And I follow "Next"
+    And I should see "Fourth chapter" in the ".book_content" "css_element"
+    And I follow "Exit book"
+    And I follow "Test book"
+    And I should see "First chapter" in the ".book_content" "css_element"

mod/book/view.php

@@ -80,7 +80,7 @@ if ($chapterid == '0') { // Go to first chapter if no given.
     book_view($book, null, false, $course, $cm, $context);
 
     foreach ($chapters as $ch) {
-        if ($edit) {
+        if ($edit || ($ch->hidden && $viewhidden)) {
             $chapterid = $ch->id;
             break;
         }
@@ -132,7 +132,7 @@ $nexttitle = null;
 $navnexttitle = null;
 $last = null;
 foreach ($chapters as $ch) {
-    if (!$edit and $ch->hidden) {
+    if (!$edit and ($ch->hidden && !$viewhidden)) {
         continue;
     }
     if ($last == $chapter->id) {