I was wrong in assuming that String had to survive long enough to avoid
it, what actually needed to survive was the CharString obtained from the
acsii() or utf8() function.
At least according to valgrind
Coming from strncpy might get you a non-NULL terminated buffer.
The solution, if you accept trunction, is to give one less byte to
strncpy and manually set the last char in the buffer to '\0'.
If the source string is shorter, than the buffer is padded with '\0'
automatically.
