Fix possible infinite loop in remote driver

When we take out completed calls from queue we might end up
in circular pointer. We don't want pointer to previous item
point to element taken out.

src/remote/remote_driver.c

@@ -10672,8 +10672,9 @@ remoteIOEventLoop(virConnectPtr conn,
                  */
                 VIR_DEBUG("Waking up sleep %d %p %p", tmp->proc_nr, tmp, priv->waitDispatch);
                 virCondSignal(&tmp->cond);
+            } else {
+                prev = tmp;
             }
-            prev = tmp;
             tmp = tmp->next;
         }