minor tweak in hex_decode()

src/hex.c

@@ -70,17 +70,12 @@ static inline ssize_t
 check(const char * const p, va_list ap)
 {
 	ssize_t len = 0;
-	const char *next;
 	va_list ap2;
 
-	if (p == vrt_magic_string_end)
-		return 0;
-	if (p != NULL && !isxstr(p, &len))
-		return -1;
-
 	va_copy(ap2, ap);
-	while ((next = va_arg(ap2, const char *)) != vrt_magic_string_end)
-		if (next != NULL && !isxstr(next, &len)) {
+	for (const char *s = p; s != vrt_magic_string_end;
+	     s = va_arg(ap2, const char *))
+		if (s != NULL && *s != '\0' && !isxstr(s, &len)) {
 			len = -1;
 			break;
 		}