Reduce flickering while moving windows

shell.asm

@@ -297,16 +297,24 @@ resize:
 ;  si = pointer to window structure
 move:
 	push dx
-	mov [si + window.y], bx
 
-	mov [si + window.x], cx
-	mov dx, [si + window.res_x]
-	sub [si + window.x], dx
+	mov dx, cx
+	sub dx, [si + window.res_x]
 
-	.not_underflow:
+	cmp [si + window.y], bx
+	jne .change
+	cmp [si + window.x], dx
+	jne .change
+	jmp .end
+
+	.change
+		mov [si + window.y], bx
+		mov [si + window.x], dx
+
+		call request_redraw
+
+	.end:
 	pop dx
-
-	call request_redraw
 	ret
 
 ; in: