virtio-devices: Require at least one ready queue for activation

When a guest resets a device by writing status=0 and reinitializes
without enabling queues before writing DRIVER_OK, the activation
path would collect zero ready queues and treat that as a fatal
error, killing the entire VMM process.

The PCI transport now checks that at least one queue is ready
before reporting that the device needs activation. This prevents
a spurious activation attempt that would fatally fail when no
queues are enabled.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

virtio-devices/src/transport/pci_device.rs

@@ -829,7 +829,9 @@ impl VirtioPciDevice {
     }
 
     fn needs_activation(&self) -> bool {
-        !self.device_activated.load(Ordering::SeqCst) && self.is_driver_ready()
+        !self.device_activated.load(Ordering::SeqCst)
+            && self.is_driver_ready()
+            && self.queues.iter().any(|q| q.ready())
     }
 
     pub fn dma_handler(&self) -> Option<&dyn ExternalDmaMapping> {