[PATCH] USB: Don't dereference NULL actconfig

This patch fixes a simple error in a couple of utility routines.  They
will no longer try to dereference a NULL actconfig pointer.  Also, they
will work a little better if the configuration is changed while they are
running (which should never happen anyway).

drivers/usb/core/usb.c

@@ -206,12 +206,15 @@ void usb_deregister(struct usb_driver *driver)
  */
 struct usb_interface *usb_ifnum_to_if(struct usb_device *dev, unsigned ifnum)
 {
+	struct usb_host_config *config = dev->actconfig;
 	int i;
 
-	for (i = 0; i < dev->actconfig->desc.bNumInterfaces; i++)
-		if (dev->actconfig->interface[i]->altsetting[0]
+	if (!config)
+		return NULL;
+	for (i = 0; i < config->desc.bNumInterfaces; i++)
+		if (config->interface[i]->altsetting[0]
 				.desc.bInterfaceNumber == ifnum)
-			return dev->actconfig->interface[i];
+			return config->interface[i];
 
 	return NULL;
 }
@@ -233,14 +236,17 @@ struct usb_interface *usb_ifnum_to_if(struct usb_device *dev, unsigned ifnum)
 struct usb_endpoint_descriptor *
 usb_epnum_to_ep_desc(struct usb_device *dev, unsigned epnum)
 {
+	struct usb_host_config *config = dev->actconfig;
 	int i, k;
 
-	for (i = 0; i < dev->actconfig->desc.bNumInterfaces; i++) {
+	if (!config)
+		return NULL;
+	for (i = 0; i < config->desc.bNumInterfaces; i++) {
 		struct usb_interface		*intf;
 		struct usb_host_interface	*alt;
 
-		/* only endpoints in current altseting are active */
-		intf = dev->actconfig->interface[i];
+		/* only endpoints in current altsetting are active */
+		intf = config->interface[i];
 		alt = intf->altsetting + intf->act_altsetting;
 
 		for (k = 0; k < alt->desc.bNumEndpoints; k++)