paste: Support -d '\0'

POSIX specifies that -d '\0' sets the delimiter to an empty string.

libutf/utftorunestr.c

@@ -4,10 +4,24 @@
 size_t
 utftorunestr(const char *str, Rune *r)
 {
-	size_t i, n;
+	size_t i;
+	int n;
 
 	for (i = 0; (n = chartorune(&r[i], str)) && r[i]; i++)
 		str += n;
 
 	return i;
 }
+
+size_t
+utfntorunestr(const char *str, size_t len, Rune *r)
+{
+	size_t i;
+	int n;
+	const char *end = str + len;
+
+	for (i = 0; (n = charntorune(&r[i], str, end - str)); i++)
+		str += n;
+
+	return i;
+}