Z4cow: make par set_Theta_zero work #551

Job	Run time
download-build-test (cpu, real64, debug)	10m 46s
download-build-test (cpu, real64, optimize)	15m 50s
download-build-test (cuda, real64, debug)	24m 26s
download-build-test (cuda, real64, optimize)	22m 40s
download-build-test (rocm, real64, optimize)	20m 53s
	1h 34m 35s

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