Consistently set specials[0] to 1

Consistently set specials[0] to 1

NULs in text files indicate corruption.  Additionally embedded NULs
can cause text files to be interpreted differently to the way they
appear to be when read by humans.  We addressed this for zone files
in 4bf686cf, by setting specials[0] to 1, where a corrupted zone
file was interpreted differently to the way it read.  We should
have applied this to other places where we read text files at that
time.  We are now applying this to

	bin/dnssec/dnssec-ksr.c.
	bin/tools/named-rrchecker.c
	lib/dns/dst_api.c
	lib/dns/skr.c
	lib/isccfg/parser.c

We should also apply this consistently to all code that mimics
reading text files to prevent false negatives like that reported
in #5796.  e.g. fuzz/dns_rdata_fromtext.c