Force pointer to stay on screen.

Without this change it's really easy to
accidentally send the pointer flying and not
be able to get it back.

egl-compositor.c

@@ -724,9 +724,19 @@ void
 notify_motion(struct egl_input_device *device, int x, int y)
 {
 	struct egl_surface *es;
+	struct egl_compositor *ec = device->ec;
 	const int hotspot_x = 16, hotspot_y = 16;
 	int32_t sx, sy;
 
+	if (x < 0)
+		x = 0;
+	if (y < 0)
+		y = 0;
+	if (x >= ec->width)
+		x = ec->width - 1;
+	if (y >= ec->height)
+		y = ec->height - 1;
+
 	es = pick_surface(device);
 
 	if (es) {