Generator Task crash

[Crypt97]

Issue description

Task crashing

Steps to reproduce the issue

1. Open new server
2. Generate world

OS and versions

• Altay: 3.0.7+dev
• PHP: 7.2
• Server OS: Windows 10
• Game version: 1.5.1

Crashdump, backtrace, memory dumps, plugins list or other files

12:39:51 CRITICAL > Could not execute asynchronous task GeneratorRegisterTask: Task crashed
12:39:51 CRITICAL > Error: "Access to undeclared static property: pocketmine\scheduler\AsyncWorker::$store" (EXCEPTION) in "src/pocketmine/scheduler/AsyncWorker" at line 93
12:39:51 DEBUG > #0 src/pocketmine/scheduler/AsyncTask(151): pocketmine\scheduler\AsyncWorker->saveToThreadStore(string generation.level4.manager, pocketmine\level\SimpleChunkManager object)
12:39:51 DEBUG > #1 src/pocketmine/level/generator/GeneratorRegisterTask(53): pocketmine\scheduler\AsyncTask->saveToThreadStore(string generation.level4.manager, pocketmine\level\SimpleChunkManager object)
12:39:51 DEBUG > #2 src/pocketmine/scheduler/AsyncTask(72): pocketmine\level\generator\GeneratorRegisterTask->onRun()
12:39:51 DEBUG > #3 (): pocketmine\scheduler\AsyncTask->run()

[Erkam246]

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