qemuDomainSetBlockThreshold: Call qemuBlockNodeNamesDetect only without blockdev

Make sure that we don't try to reload node names with -blockdev. If
something doesn't have a node name the update will not make the
situation better.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_driver.c

@@ -22597,7 +22597,8 @@ qemuDomainSetBlockThreshold(virDomainPtr dom,
     if (!(src = qemuDomainGetStorageSourceByDevstr(dev, vm->def)))
         goto endjob;
 
-    if (!src->nodestorage &&
+    if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV) &&
+        !src->nodestorage &&
         qemuBlockNodeNamesDetect(driver, vm, QEMU_ASYNC_JOB_NONE) < 0)
         goto endjob;