[BUGFIX] Reset global ajaxID for ajax requests

Due to patch https://review.typo3.org/#/c/37409/ the global ajaxID
isn't set anymore. This variable is needed by several ajax requests and
expected to be set in global context. This patch sets the given ajaxID
globally.

Releases: master
Resolves: #65477
Change-Id: Id06d9b6a4d7bf41061e917ed6049a3dfefbf32f0
Reviewed-on: http://review.typo3.org/37493


Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>

typo3/sysext/backend/Classes/AjaxRequestHandler.php

@@ -72,6 +72,7 @@ class AjaxRequestHandler implements RequestHandlerInterface {
 			define('TYPO3_PROCEED_IF_NO_USER', 2);
 		}
 
+		$GLOBALS['ajaxID'] = $ajaxID;
 		$this->bootstrap
 			->checkLockedBackendAndRedirectOrDie()
 			->checkBackendIpOrDie()