flacenc: Fix handling of image tags
flacenc: Fix handling of image tags

The caps should be used to get the mimetype and there is
only an info structure for the GstSample if the image-type
is not NONE.

Distrotech/gst-plugins-good,Distrotech/gst-plugins-good,Distrotech/gst-plugins-good,Distrotech/gst-plugins-good,Distrotech/gst-plugins-good