oniguruma: Out-of-bounds stack write in onigenc_unicode_get_case_fold_codes_by_str() during regular expression compilation

An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A stack out-of-bounds write in onigencunicodegetcasefoldcodesbystr occurs during regular expression compilation. Code point 0xFFFFFFFF is not properly handled in...