MDL-49399 core: Allow creation of a new per-request basedir

Shutdown handlers are processed in order. If something in a shutdown
handler uses a file which is stored in a per-request directory, and
another, unrelated, per-request directory was created before the handler
started. then a fresh per-request directory will be required.

lib/classes/task/logmanager.php

@@ -89,8 +89,7 @@ class logmanager {
         }
 
         // We register a shutdown handler to ensure that logs causing any failures are correctly disposed of.
-        // Note: This must happen before the per-request directory is requested because the shutdown handler may delete
-        // the logfile.
+        // Note: This must happen before the per-request directory is requested because the shutdown handler deletes the logfile.
         if (!self::$tasklogregistered) {
             \core_shutdown_manager::register_function(function() {
                 // These will only actually do anything if capturing is current active when the thread ended, which
@@ -98,6 +97,9 @@ class logmanager {
                 \core\task\logmanager::finalise_log(true);
             });
 
+            // Create a brand new per-request directory basedir.
+            get_request_storage_directory(true, true);
+
             self::$tasklogregistered = true;
         }