usb: add device checks before redirector calls to usb_ep_get()

Add an assert and an explicit check before the two callers to
usb_ep_get() in the USB redirector code to ensure the device
passed in is not NULL.
Signed-off-by: NLiam Merwick <liam.merwick@oracle.com>
Message-id: 1549460216-25808-9-git-send-email-liam.merwick@oracle.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/redirect.c

@@ -1728,6 +1728,7 @@ static void usbredir_ep_info(void *priv,
     USBRedirDevice *dev = priv;
     int i;
 
+    assert(dev != NULL);
     for (i = 0; i < MAX_ENDPOINTS; i++) {
         dev->endpoint[i].type = ep_info->type[i];
         dev->endpoint[i].interval = ep_info->interval[i];
@@ -2125,7 +2126,7 @@ static int usbredir_post_load(void *priv, int version_id)
 {
     USBRedirDevice *dev = priv;
 
-    if (dev->parser == NULL) {
+    if (dev == NULL || dev->parser == NULL) {
         return 0;
     }