qemu: checkpoint: Do ACL check prior to snapshot interlocking

The interlocking with snapshots is executed prior to the ACL check so if
a VM has snapshots invoking the checkpoint API may leak it's existance.

Introduced with the qemuDomainCheckpointCreateXML API implementation in
commit 5f4e0796.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>

src/qemu/qemu_driver.c

@@ -17254,18 +17254,18 @@ qemuDomainCheckpointCreateXML(virDomainPtr domain,
     if (!(vm = qemuDomainObjFromDomain(domain)))
         goto cleanup;
 
-    if (virDomainSnapshotObjListNum(vm->snapshots, NULL, 0) > 0) {
-        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
-                       _("cannot create checkpoint while snapshot exists"));
-        goto cleanup;
-    }
-
     priv = vm->privateData;
     cfg = virQEMUDriverGetConfig(driver);
 
     if (virDomainCheckpointCreateXMLEnsureACL(domain->conn, vm->def, flags) < 0)
         goto cleanup;
 
+    if (virDomainSnapshotObjListNum(vm->snapshots, NULL, 0) > 0) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                       _("cannot create checkpoint while snapshot exists"));
+        goto cleanup;
+    }
+
     if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BITMAP_MERGE)) {
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                        _("qemu binary lacks persistent bitmaps support"));