AD fix for PDBijector #478

Job	Run time
test (1.6, ubuntu-latest, x64, ForwardDiff)	6m 49s
test (1.6, ubuntu-latest, x64, Tracker)	5m 20s
test (1.6, ubuntu-latest, x64, ReverseDiff)	6m 16s
test (1.6, ubuntu-latest, x64, Zygote)	6m 38s
test (1.6, macOS-latest, x64, ForwardDiff)	6m 55s
test (1.6, macOS-latest, x64, Tracker)	5m 35s
test (1.6, macOS-latest, x64, ReverseDiff)	8m 43s
test (1.6, macOS-latest, x64, Zygote)	7m 26s
test (1, ubuntu-latest, x64, ForwardDiff)	5m 39s
test (1, ubuntu-latest, x64, Tracker)	5m 30s
test (1, ubuntu-latest, x64, ReverseDiff)	6m 13s
test (1, ubuntu-latest, x64, Zygote)	6m 48s
test (1, macOS-latest, x64, ForwardDiff)	7m 7s
test (1, macOS-latest, x64, Tracker)	6m 47s
test (1, macOS-latest, x64, ReverseDiff)	8m 11s
test (1, macOS-latest, x64, Zygote)	7m 42s
	1h 47m 39s

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