virtio/vhost-user: Fix wrong vhost notifier GPtrArray size

virtio/vhost-user: Fix wrong vhost notifier GPtrArray size

In fetch_or_create_notifier, idx begins with 0. So the GPtrArray size
should be idx + 1 and g_ptr_array_set_size should be called with idx + 1.

This wrong GPtrArray size causes fetch_or_create_notifier return an invalid
address. Passing this invalid pointer to vhost_user_host_notifier_remove
causes assert fail:

    qemu/include/qemu/int128.h:27: int128_get64: Assertion `r == a' failed.
	shutting down, reason=crashed

Backends like dpdk-vdpa which sends out vhost notifier requests almost always
hit qemu crash.

Fixes: 503e355465 ("virtio/vhost-user: dynamically assign VhostUserHostNotifiers")
Signed-off-by: Yajun Wu <yajunw@nvidia.com>
Acked-by: Parav Pandit <parav@nvidia.com>
Change-Id: I87e0f7591ca9a59d210879b260704a2d9e9d6bcd
Message-Id: <20220526034851.683258-1-yajunw@nvidia.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Eddie Dong <eddie.dong@intel.com>