printf(): Print null pointers (arg for %s = 0) as (null), fixes #4

src/tests.asm

@@ -109,6 +109,8 @@ section .rodata
 	printf16Str		db	"%x | %#10x | %10x | %#10x | %010x | %#010x\n",EOS
 	printf17		db	TAB,"printf(",DQUO,"Ran\dom in\v\a\li%\d test%\n",DQUO,"): ",NL,TAB,TAB,EOS
 	printf17Str		db	"Ran\dom in\v\a\li%\d test%\n",EOS
+	printf18		db	TAB,"printf(",DQUO,"atoi(12345, 9, 0, 0): %s <<should print (null)\n",DQUO,", atoi(12345, 9, 0, 0)):",NL,TAB,TAB,EOS
+	printf18Str		db	"atoi(12345, 9, 0, 0): %s <<should print (null)\n",EOS
 	; strlen()
 	msgStrlen		db	NL,"TEST strlen()",NL,EOS
 	strlen1			db	TAB,"strlen(str1): %d",NL,EOS
@@ -447,10 +449,24 @@ _start:
 	call	printf
 	add	rsp, SIZE_QWORD * 2
 
+	; TEST 17
 	lea	rdi, [rel printf17]
 	call	print
 	lea	rdi, [rel printf17Str]
 	call	printf
+
+	; TEST 18
+	lea	rdi, [rel printf18]
+	call	print
+
+	mov	rdi, 12345
+	mov	rsi, 9
+	xor	rdx, rdx
+	xor	rcx, rcx
+	call	itoa
+	lea	rdi, [rel printf18Str]
+	mov	rsi, rax
+	call	printf
 %endif
 
 ;---