Get only recent Thumbnail-Posts

hi,

i try to get the recent post ONLY WITH a post-thumbnail. that means if there is a post with no thumbnail the last post WITH a thumbnail should be displayed.

this is my code so far to display the last post (in a sidebar) from a custom post type / taxonomy:

[Code moderated as per the Forum Rules. The maximum number of lines of code that you can post in these forums is ten lines. Please use the pastebin]

this works fine. but now when i add a new post without a thumbnail nothing is displayed anymore of course…

so how can i display the last post with a post-thumb attached?

thanks sooo much in advance for help ??