ICU-22580 Address infinity loop in RBBI #1305

Job	Run time
clang-valgrind-intltest (utility)	6m 39s
clang-valgrind-test	9m 56s
clang-valgrind-intltest (normalize)	6m 19s
clang-valgrind-intltest (collator)	5m 9s
clang-valgrind-intltest (regex)	5m 11s
clang-valgrind-intltest (format)	16m 29s
clang-valgrind-intltest (translit)	5m 59s
clang-valgrind-intltest (rbbi)	6m 49s
clang-valgrind-intltest (rbnf)	6m 17s
clang-valgrind-intltest (rbnfrt)	6m 25s
clang-valgrind-intltest (icuserv)	4m 53s
clang-valgrind-intltest (idna)	5m 9s
clang-valgrind-intltest (convert)	6m 30s
clang-valgrind-intltest (rbnfp)	5m 16s
clang-valgrind-intltest (csdet)	5m 9s
clang-valgrind-intltest (spoof)	4m 45s
clang-valgrind-intltest (bidi)	5m 25s
	1h 52m 20s

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