ICU-22555 Fix infinity loop in RuleBasedCollator constructor #1113

Job	Run time
clang-valgrind-test	16m 44s
clang-valgrind-intltest (utility)	10m 8s
clang-valgrind-intltest (normalize)	9m 14s
clang-valgrind-intltest (collator)	6m 4s
clang-valgrind-intltest (regex)	7m 15s
clang-valgrind-intltest (format)	25m 54s
clang-valgrind-intltest (translit)	9m 26s
clang-valgrind-intltest (rbbi)	11m 32s
clang-valgrind-intltest (rbnf)	11m 29s
clang-valgrind-intltest (rbnfrt)	7m 58s
clang-valgrind-intltest (icuserv)	7m 42s
clang-valgrind-intltest (idna)	8m 19s
clang-valgrind-intltest (convert)	7m 53s
clang-valgrind-intltest (rbnfp)	7m 20s
clang-valgrind-intltest (csdet)	6m 1s
clang-valgrind-intltest (spoof)	8m 23s
clang-valgrind-intltest (bidi)	6m 24s
	2h 47m 46s

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