Allow moving windows off the left side of screen

shell.asm

@@ -158,11 +158,19 @@ paint:
 	mov cx, bx
 	add cx, di
 	cmp cx, COLUMNS
-	jle .no_clipping_width
+	jle .no_clipping_width_right
 	mov cx, COLUMNS
-	.no_clipping_width:
+	.no_clipping_width_right:
 	sub cx, di
 
+	cmp di, 0
+	jge .no_clipping_width_left
+	sub si, di
+	sub si, di
+	add cx, di
+	xor di, di
+	.no_clipping_width_left:
+
 	call PONYDOS_SEG:SYS_DRAW_RECT
 
 	ret
@@ -294,9 +302,6 @@ move:
 	mov [si + window.x], cx
 	mov dx, [si + window.res_x]
 	sub [si + window.x], dx
-	jnc .not_underflow
-
-	mov word [si + window.x], 0
 
 	.not_underflow:
 	pop dx