Use strlcpy() in favor of strncpy() as it's defined to have a nul character

Use strlcpy() in favor of strncpy() as it's defined to have a nul character
at the end of string buffer, and the code context do expects this to behave
correctly (e.g. strchr).

Note that we do not believe there is real-world impact for gstat(8)'s usage
because the strings are length checked, and the on-stack buffer belongs to
main() and we can expect to have zeros in them.

MFC after:	2 weeks