[PATCH] virtio-pci: add check for vdev in virtio_pci_isr_read

[Yuri Benditovich]

https://bugzilla.redhat.com/show_bug.cgi?id=1743098
There is missing check for vdev in this procedure.
QEMU crash happens in it in hot unplug flow.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
---
 hw/virtio/virtio-pci.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 094c36aa3e..2f19301267 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1364,7 +1364,13 @@ static uint64_t virtio_pci_isr_read(void *opaque, hwaddr 
addr,
 {
     VirtIOPCIProxy *proxy = opaque;
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
-    uint64_t val = qatomic_xchg(&vdev->isr, 0);
+    uint64_t val = 0;
+
+    if (vdev == NULL) {
+        return val;
+    }
+
+    val = qatomic_xchg(&vdev->isr, 0);
     pci_irq_deassert(&proxy->pci_dev);
 
     return val;
-- 
2.17.1