main: Fix playback from some sources

Sources that require resolve() to be called to get the actual
playback URL didn't work correctly, as we didn't request the
external URL.
main: Debug for search results
main: Remove FIXME

We don't need to unref() the popover as it gets attached to its
"pointing-to" widget a-la gtk_container_add, so gtk_widget_destroy()
on the parent will take care of destroying it.

Above explanation paraphrased from Carlos Garnacho.