libpromises/evalfunction: Do not crash w/o arguments (3.21.x) #1760

Job	Run time
unit_tests / Run Unit Tests	2m 38s
shellcheck_tests / Run shellcheck on shell scripts	1m 10s
valgrind_check / valgrind_check	4m 25s
macos_unit_tests / macos_unit_tests	2m 39s
acceptance_tests / acceptance_tests	27m 39s
asan_unit_tests / asan_unit_tests	2m 38s
static_check / static_check	6m 39s
	47m 48s

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