Verify parent_dev before udev_device_get_sysattr_value

Fixes: #16705

Not all udev devices have parent devices.
Calling udev_device_get_ functions yield an assertion error
if called with a NULL pointer.

Changes to be committed:
	modified:   cmd/zed/zed_disk_event.c

Signed-off-by: Sietse <[email protected]>

Author: Sietse

cmd/zed/zed_disk_event.c

@@ -139,7 +139,8 @@ dev_event_nvlist(struct udev_device *dev)
 		 * is /dev/sda.
 		 */
 		struct udev_device *parent_dev = udev_device_get_parent(dev);
-		if ((value = udev_device_get_sysattr_value(parent_dev, "size"))
+		if (parent_dev != NULL &&
+            (value = udev_device_get_sysattr_value(parent_dev, "size"))
 		    != NULL) {
 			uint64_t numval = DEV_BSIZE;