staging: r8712u: Check pointer before use

Routine r8712_usb_read_port() dereferences "precvbuf" before testing it
for NULL.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/usb_ops_linux.c

@@ -270,14 +270,13 @@ u32 r8712_usb_read_port(struct intf_hdl *pintfhdl, u32 addr, u32 cnt, u8 *rmem)
 	struct usb_device *pusbd = pdvobj->pusbdev;
 
 	if (adapter->bDriverStopped || adapter->bSurpriseRemoved ||
-	    adapter->pwrctrlpriv.pnp_bstop_trx)
+	    adapter->pwrctrlpriv.pnp_bstop_trx || !precvbuf)
 		return _FAIL;
 	if (precvbuf->reuse || !precvbuf->pskb) {
 		precvbuf->pskb = skb_dequeue(&precvpriv->free_recv_skb_queue);
 		if (precvbuf->pskb != NULL)
 			precvbuf->reuse = true;
 	}
-	if (precvbuf != NULL) {
 	r8712_init_recvbuf(adapter, precvbuf);
 	/* re-assign for linux based on skb */
 	if (!precvbuf->reuse || !precvbuf->pskb) {
@@ -312,9 +311,6 @@ u32 r8712_usb_read_port(struct intf_hdl *pintfhdl, u32 addr, u32 cnt, u8 *rmem)
 	err = usb_submit_urb(purb, GFP_ATOMIC);
 	if ((err) && (err != (-EPERM)))
 		ret = _FAIL;
-	} else {
-		ret = _FAIL;
-	}
 	return ret;
 }