rbd: skip unmap if device is not mapped

PVE/Storage/RBDPlugin.pm

@@ -510,6 +510,8 @@ sub deactivate_volume {
     my $pool =  $scfg->{pool} ? $scfg->{pool} : 'rbd';
 
     my $path = "/dev/rbd/$pool/$name";
+    return if ! -b $path;
+
     my $cmd = &$rbd_cmd($scfg, $storeid, 'unmap', $path);
     run_rbd_command($cmd, errmsg => "can't unmount rbd volume $name");