icu: Use-of-uninitialized-value in u_strToUTF8WithSub_59

Detailed report: https://oss-fuzz.com/testcase?key=6488436909277184 Project: icu Fuzzer: libFuzzericuucasemapfuzzer Fuzz target binary: ucasemapfuzzer Job Type: libfuzzermsanicu Platform Id: linux Crash Type: Use-of-uninitialized-value Crash Address: Crash State: ustrToUTF8WithSub59 ustrToUTF859...