analyzer: fix member call on null seen with ubsan [PR97178]

analyzer: fix member call on null seen with ubsan [PR97178]

gcc/analyzer/ChangeLog:
	PR analyzer/97178
	* engine.cc (impl_run_checkers): Update for change to ext_state
	ctor.
	* program-state.cc (selftest::test_sm_state_map): Pass an engine
	instance to ext_state ctor.
	(selftest::test_program_state_1): Likewise.
	(selftest::test_program_state_2): Likewise.
	(selftest::test_program_state_merging): Likewise.
	(selftest::test_program_state_merging_2): Likewise.
	* program-state.h (extrinsic_state::extrinsic_state): Remove NULL
	default value for "eng" param.