In cgetmatch(3), return -1 if a NULL or 0-length name parameter is used.

This situation most notably arises in chkprintcap, when a /etc/printcap
entry has an empty rp= attribute. In that case, cgetmatch would enter
an infinite loop if any entry in the file has multiple names.

This causes lpd to hang at boot time on 5.0-DP2 when both conditions
are met (:rp=: and multiple names -- not necessarily on the same entry).

Reviewed by:	roberto

lib/libc/gen/getcap.c

@@ -577,6 +577,9 @@ cgetmatch(const char *buf, const char *name)
 {
 	const char *np, *bp;
 
+	if (name == NULL || *name == '\0')
+		return -1;
+
 	/*
 	 * Start search at beginning of record.
 	 */