Activity tasks - don't add invalid tasks

Instead of 'handling the task code building invalid tasks - civicrm#20945' - this proposes to only attempt
to add a page if it is for a valid task. This keeps the grouchiness in the generic controller
to warn us of other mistakes.

This code is pretty fugly! However, it really is just called internally within this class.

CRM/Activity/StateMachine/Search.php

@@ -35,16 +35,10 @@ public function __construct($controller, $action = CRM_Core_Action::NONE) {
     $this->_pages = [];
 
     $this->_pages['CRM_Activity_Form_Search'] = NULL;
-    list($task, $result) = $this->taskName($controller, 'Search');
+    list($task) = $this->taskName($controller, 'Search');
     $this->_task = $task;
-
-    if (is_array($task)) {
-      foreach ($task as $t) {
-        $this->_pages[$t] = NULL;
-      }
-    }
-    else {
-      $this->_pages[$task] = NULL;
+    foreach ($task as $t) {
+      $this->_pages[$t] = NULL;
     }
 
     $this->addSequentialPages($this->_pages, $action);
@@ -63,7 +57,7 @@ public function __construct($controller, $action = CRM_Core_Action::NONE) {
    * @return array
    *   the name of the form that will handle the task
    */
-  public function taskName($controller, $formName = 'Search') {
+  protected function taskName($controller, $formName = 'Search') {
     // total hack, check POST vars and then session to determine stuff
     $value = $_POST['task'] ?? NULL;
     if (!isset($value)) {

CRM/Activity/Task.php

@@ -156,11 +156,10 @@ public static function getTask($value) {
       // make the print task by default
       $value = self::TASK_PRINT;
     }
-
-    return [
-      self::$_tasks[$value]['class'],
-      self::$_tasks[$value]['result'],
-    ];
+    if (isset(self::$_tasks[$value])) {
+      return [self::$_tasks[$value]['class'], self::$_tasks[$value]['result']];
+    }
+    return [[]];
   }
 
 }