qemu: backup: Move capability check after inactive check

Inactive VM doesn't have qemuCaps set thus we'd never properly report
that VM backups are supported only for running VMs.

Move the capability check after the active check.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/qemu/qemu_backup.c

@@ -750,12 +750,6 @@ qemuBackupBegin(virDomainObjPtr vm,
 
     virCheckFlags(VIR_DOMAIN_BACKUP_BEGIN_REUSE_EXTERNAL, -1);
 
-    if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_INCREMENTAL_BACKUP)) {
-        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
-                       _("incremental backup is not supported yet"));
-        return -1;
-    }
-
     if (!(def = virDomainBackupDefParseString(backupXML, priv->driver->xmlopt, 0)))
         return -1;
 
@@ -793,6 +787,12 @@ qemuBackupBegin(virDomainObjPtr vm,
         goto endjob;
     }
 
+    if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_INCREMENTAL_BACKUP)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                       _("incremental backup is not supported yet"));
+        goto endjob;
+    }
+
     if (priv->backup) {
         virReportError(VIR_ERR_OPERATION_INVALID, "%s",
                        _("another backup job is already running"));