[Bug c++/92919] invalid memory access in wide_str_to_charconst when running ucn2.C testcase (caught by hwasan)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92919

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
valgrind reports this too:
==31127== Invalid read of size 1
==31127==    at 0x2594AFA: wide_str_to_charconst (charset.c:1980)
==31127==    by 0x2594AFA: cpp_interpret_charconst(cpp_reader*, cpp_token
const*, unsigned int*, int*) (charset.c:2045)
==31127==    by 0xCE5C02: lex_charconst(cpp_token const*) (c-lex.c:1373)
==31127==    by 0xCE3990: c_lex_with_flags(tree_node**, unsigned int*, unsigned
char*, int) (c-lex.c:617)
==31127==    by 0xAC982C: cp_lexer_get_preprocessor_token(cp_lexer*, cp_token*)
(parser.c:807)
==31127==    by 0xAC94B5: cp_lexer_new_main() (parser.c:654)
==31127==    by 0xACD972: cp_parser_new() (parser.c:3969)
==31127==    by 0xB2E00F: c_parse_file() (parser.c:43064)
==31127==    by 0xCF6495: c_common_parse_file() (c-opts.c:1186)
==31127==    by 0x15141F6: compile_file() (toplev.c:458)
==31127==    by 0x1517382: do_compile() (toplev.c:2267)
==31127==    by 0x151767A: toplev::main(int, char**) (toplev.c:2406)
==31127==    by 0x251E0F9: main (main.c:39)
==31127==  Address 0x51084af is 1 bytes before a block of size 2 alloc'd
==31127==    at 0x483AD19: realloc (vg_replace_malloc.c:836)
==31127==    by 0x25E0E6C: xrealloc (xmalloc.c:179)
==31127==    by 0x2593C4C: cpp_interpret_string_1(cpp_reader*, cpp_string
const*, unsigned long, cpp_string*, cpp_ttype, cpp_string_location_reader*,
cpp_substring_ranges*) (charset.c:1753)
==31127==    by 0x2594A30: cpp_interpret_string (charset.c:1784)
==31127==    by 0x2594A30: cpp_interpret_charconst(cpp_reader*, cpp_token
const*, unsigned int*, int*) (charset.c:2036)
==31127==    by 0xCE5C02: lex_charconst(cpp_token const*) (c-lex.c:1373)
==31127==    by 0xCE3990: c_lex_with_flags(tree_node**, unsigned int*, unsigned
char*, int) (c-lex.c:617)
==31127==    by 0xAC982C: cp_lexer_get_preprocessor_token(cp_lexer*, cp_token*)
(parser.c:807)
==31127==    by 0xAC94B5: cp_lexer_new_main() (parser.c:654)
==31127==    by 0xACD972: cp_parser_new() (parser.c:3969)
==31127==    by 0xB2E00F: c_parse_file() (parser.c:43064)
==31127==    by 0xCF6495: c_common_parse_file() (c-opts.c:1186)
==31127==    by 0x15141F6: compile_file() (toplev.c:458)