OSV-2021-1785 Heap-use-after-free in ut_allocator<os_event>::allocate

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=43059 Crash type: Heap-use-after-free READ 8 Crash state: utallocator::allocate oseventcreate rwlockcreatefunc...