fcup-smsend[mult]: fix buglet in K&R C NULL pointer passing The only 100% safe way to pass a NULL pointer as a function argument in K&R C is to cast 0 to a pointer type; failing to do so may cause mysterious bugs (invalid stack frames or garbage in argument registers) on 64-bit machines. This issue has already been fixed in most of FC host tools, but I just found some missed spots: passing of NULL UDH to PDU encoding functions in fcup-smsend[mult] in the case of single (not concatenated) SMS.

/*
 * Data structures for parsing structured responses to AT commands
 */

struct resp_field {
	int		type;
	unsigned	num;
	char		*str;
};

#define	RESP_FIELD_EMPTY	0
#define	RESP_FIELD_NUMBER	1
#define	RESP_FIELD_STRING	2