[mythtv] Recording preview picture not updated sometimes

[Thomas Börkel]

HI!

I have enabled the recording preview picture (not live preview).

When I navigate through the recordings in the playback screen, sometimes
the preview picture is not being updated. So, I navigate from recording
to recording and the picture is always the same.

After some navigating up and down, it starts updating the picture again.

I am using 0.15.1 and this did not happen in 0.14.

Thomas