ICU-22830 Fix memLeak in numrange_fluent.cpp #2472

Job	Run time
clang-valgrind-intltest (utility)	6m 39s
clang-valgrind-test	10m 14s
clang-valgrind-intltest (normalize)	6m 2s
clang-valgrind-intltest (collator)	5m 45s
clang-valgrind-intltest (regex)	5m 15s
clang-valgrind-intltest (format)	16m 26s
clang-valgrind-intltest (translit)	5m 44s
clang-valgrind-intltest (rbbi)	7m 20s
clang-valgrind-intltest (rbnf)	6m 38s
clang-valgrind-intltest (rbnfrt)	6m 19s
clang-valgrind-intltest (icuserv)	4m 52s
clang-valgrind-intltest (idna)	4m 46s
clang-valgrind-intltest (convert)	6m 35s
clang-valgrind-intltest (rbnfp)	5m 6s
clang-valgrind-intltest (csdet)	5m 8s
clang-valgrind-intltest (spoof)	5m 20s
clang-valgrind-intltest (bidi)	5m 13s
	1h 53m 22s

Provide feedback