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.

	.text
	.code	32
	.globl	strlen
strlen:
	mov	r1, r0
1:	ldrb	r2, [r0], #1
	cmn	r2, #0
	bne	1b
	sbc	r0, r0, r1
	bx	lr