Use strlcpy() instead of strncpy() when copying the encoding value

Use strlcpy() instead of strncpy() when copying the encoding value
to ensure that the destination is NUL terminated.  Length truncation
of one more character should not be an issue since encoding values
that long are not supported by libc.  The destination string is
treated as a NUL terminated string, but it is only passed to strcmp()
for comparison to a set of shorter, fixed length strings, so this
is not a serious problem.

Reported by:	Coverity
CID:		974769
MFC after:	1 week