[XFA] Thread Tabs - XF2 2.6.0

Corrected bugs:

• Template errors
  Template public:xfa_ttabs_thread_view: Cannot call method getTabs on a non-object (NULL) (src/XF/Template/Templater.php:927)
  Template public:xfa_ttabs_thread_view: Cannot call method canAddXfaTabs on a non-object (NULL) (src/XF/Template/Templater.php:927)