analyzer: fix uninit in null-termination checking [PR124055]

analyzer: fix uninit in null-termination checking [PR124055]

gcc/analyzer/ChangeLog:
	PR analyzer/124055
	* kf.cc (kf_strcpy::impl_call_pre): Ensure bytes_to_copy is
	initialized.  Assert that it was written to with non-null if
	check_for_null_terminated_string_arg returns non-null.
	* region-model.cc (region_model::scan_for_null_terminator):
	Initialize *out_sval, and assert it is written to when
	returning non-null.
	(region_model::check_for_null_terminated_string_arg): Assert
	that scan_for_null_terminator wrote to *out_sval if it
	returns non-null.

gcc/testsuite/ChangeLog:
	PR analyzer/124055
	* gcc.dg/analyzer/ice-pr124055-1.c: New test.
	* gcc.dg/analyzer/ice-pr124055-2.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>