When Swift::LibIDNConverter::getStringPrepared was called with an input of 1024 or more characters, stringprep would be called on a memory region that wasn't NUL-terminated. It also blindly trimmed the input to 1024 bytes, even though there may be input longer than that that still results in a valid 1023 byte prepped string. IDNConverterTest has been converted to gtest, as cppunit cannot deal with testing for std::exceptions being thrown on at least macOS Test-Information: Unit tests pass on macOS 10.13 and Debian 9 Before fix, the newly added unit tests triggered an ASan abort due to a buffer overrun. After fix, all unit tests pass, even with ASan enabled. Change-Id: Ia3e51a39f5db1de32b8f8bb388f81ca041136df7