harden World unique object handling #1612

Job	Run time
macos-latest: clang++ Release Threads	18m 39s
macos-latest: clang++ Release OneTBB	3m 38s
macos-latest: clang++ Release PaRSEC	3m 55s
ubuntu-20.04: /usr/bin/g++-9 Release Threads	30m 59s
ubuntu-20.04: /usr/bin/g++-9 Release OneTBB	1m 41s
ubuntu-20.04: /usr/bin/g++-9 Release PaRSEC	1m 48s
macos-latest: clang++ Debug Threads	45m 8s
macos-latest: clang++ Debug OneTBB	4m 11s
macos-latest: clang++ Debug PaRSEC	3m 11s
ubuntu-20.04: /usr/bin/g++-9 Debug Threads	44m 44s
ubuntu-20.04: /usr/bin/g++-9 Debug OneTBB	1m 45s
ubuntu-20.04: /usr/bin/g++-9 Debug PaRSEC	2m 0s
	2h 41m 39s

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