Replace `strlcpy` with `strncpy` in `msIO_stripStdoutBufferContentType()`

The use of `strlcpy` was producing *uninitialised value* errors in
valgrind.  It appears this was due to the fact that `strlcpy` expects
the source string to be null terminated which is not always the case
in this context.
Merge branch 'branch-6-2'