ICU-22832 Fix msan complain about use-of-uninitialized-value #2407

Job	Run time
clang-valgrind-test	9m 42s
clang-valgrind-intltest (utility)	8m 26s
clang-valgrind-intltest (normalize)	7m 16s
clang-valgrind-intltest (collator)	6m 42s
clang-valgrind-intltest (regex)	6m 12s
clang-valgrind-intltest (format)	16m 46s
clang-valgrind-intltest (translit)	6m 11s
clang-valgrind-intltest (rbbi)	7m 18s
clang-valgrind-intltest (rbnf)	6m 18s
clang-valgrind-intltest (rbnfrt)	7m 0s
clang-valgrind-intltest (icuserv)	5m 35s
clang-valgrind-intltest (idna)	5m 50s
clang-valgrind-intltest (convert)	6m 29s
clang-valgrind-intltest (rbnfp)	5m 12s
clang-valgrind-intltest (csdet)	5m 29s
clang-valgrind-intltest (spoof)	5m 32s
clang-valgrind-intltest (bidi)	6m 43s
	2h 2m 41s

Provide feedback