Fix undefined behavior front() call
Cherry pick undefined behavior fix from ICU PR3752

Upstream fix https://github.com/unicode-org/icu/pull/3752

Bug: 451657601
Change-Id: I2d7bad25d0c924dd57e63dce342e5e2e08cfe224
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/7099182
Reviewed-by: Philip Jägenstedt <[email protected]>
5 files changed