qemu: ignore query-sev-capabilities errors

The query-sev-capabilities command fails if SEV is not compiled in,
even though both the command and -object sev-guest are present
in that case :/

Ignore the errors to avoid spamming the logs:
internal error: unable to execute QEMU command 'query-sev-capabilities': SEV feature is not available
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>

src/qemu/qemu_monitor_json.c

@@ -6423,6 +6423,12 @@ qemuMonitorJSONGetSEVCapabilities(qemuMonitorPtr mon,
     if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
         goto cleanup;
 
+    /* Both -object sev-guest and query-sev-capabilities can be present
+     * even if SEV is not available */
+    if (qemuMonitorJSONHasError(reply, "GenericError")) {
+        ret = 0;
+        goto cleanup;
+    }
 
     if (qemuMonitorJSONCheckError(cmd, reply) < 0)
         goto cleanup;