icu: add upstream security fix for utf-8 handling

icu: add upstream security fix for utf-8 handling

Fixes:

CVE-2017-7867 - International Components for Unicode (ICU) for C/C++ before
2017-02-13 has an out-of-bounds write caused by a heap-based buffer overflow
related to the utf8TextAccess function in common/utext.cpp and the
utext_setNativeIndex* function.

CVE-2017-7868 - International Components for Unicode (ICU) for C/C++ before
2017-02-13 has an out-of-bounds write caused by a heap-based buffer overflow
related to the utf8TextAccess function in common/utext.cpp and the
utext_moveIndex32* function.

Upstream: http://bugs.icu-project.org/trac/changeset/39671

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>