__INTERNAL_fmt: Exit if syscall NR_write fails (which is very likely if called through fwrite with an invalid FD)

src/console.asm

@@ -457,6 +457,8 @@ __INTERNAL_fmt:
 	pop	rdx
 	pop	rsi
 	pop	rdi
+	test	rax, rax
+	js	.quit
 	xor	r10, r10
 
 	cmp	r9b, 0
@@ -475,6 +477,8 @@ __INTERNAL_fmt:
 	mov	rdx, r10
 	mov	r10, r11
 	syscall
+	test	rax, rax
+	js	.quit
 	mov	rax, r10
 	jmp	.quit