analyzer: fix ICE with -fsanitize=undefined [PR98293]

analyzer: fix ICE with -fsanitize=undefined [PR98293]

-fsanitize=undefined with calls to nonnull functions
creates struct __ubsan_nonnull_arg_data instances
with CONSTRUCTORs for RECORD_TYPEs with NULL index values.
The analyzer was mistakenly using INTEGER_CST for these
fields, leading to ICEs.

Fix the issue by iterating through the fields in the type
for such cases, imitating similar logic in varasm.c's
output_constructor.

gcc/analyzer/ChangeLog:
	PR analyzer/98293
	* store.cc (binding_map::apply_ctor_to_region): When "index" is
	NULL, iterate through the fields for RECORD_TYPEs, rather than
	creating an INTEGER_CST index.

gcc/testsuite/ChangeLog:
	PR analyzer/98293
	* gcc.dg/analyzer/pr98293.c: New test.