ticket:11370 Regex, add missing range check of length of a look-behind expression.

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@36724 251d0590-4201-4cf1-90de-194747b24ca1
ticket:11369 Regex, fix incorrect optimization of patterns with a zero length quantifier {0}

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@36727 251d0590-4201-4cf1-90de-194747b24ca1