Cherrypick fix for SEGV_MAPERR

Avoid int32_t overflow in length addition

See
https://bugs.chromium.org/p/chromium/issues/detail?id=1044570
https://unicode-org.atlassian.net/browse/ICU-20958
https://github.com/unicode-org/icu/pull/971

Bug: chromium:1044570
Change-Id: I52ef1545007d708315e1fd8265ec42d1c706feed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2036290
Reviewed-by: Jungshik Shin <jshin@chromium.org>
3 files changed