ICU-22584 Fix derefence of nullptr #1309

Job	Run time
clang-valgrind-intltest (utility)	6m 45s
clang-valgrind-intltest (normalize)	6m 15s
clang-valgrind-intltest (collator)	5m 2s
clang-valgrind-test	10m 3s
clang-valgrind-intltest (regex)	5m 3s
clang-valgrind-intltest (format)	16m 7s
clang-valgrind-intltest (translit)	5m 57s
clang-valgrind-intltest (rbbi)	7m 48s
clang-valgrind-intltest (rbnf)	6m 25s
clang-valgrind-intltest (rbnfrt)	6m 18s
clang-valgrind-intltest (icuserv)	5m 21s
clang-valgrind-intltest (idna)	5m 55s
clang-valgrind-intltest (convert)	6m 49s
clang-valgrind-intltest (rbnfp)	5m 16s
clang-valgrind-intltest (csdet)	5m 35s
clang-valgrind-intltest (spoof)	5m 2s
clang-valgrind-intltest (bidi)	5m 45s
	1h 55m 26s

Provide feedback