Show thumbnail image in edit view if baseUrl is set in opts

[ddresch]

Without this patch, the edit view is not displaying uploaded images in the dropzone, which is ignoring the opts parameter. With a set baseUrl (e.g. '/files') you end up with URLs like this:

http://localhost:3000/public/files/63eff0d95e1575f0ef32d9c9/arc.png 

This PR adds the needed check if baseUrl is defined in the opts object.

Additionally (sorry mixed it up with this PR) a quick check is added if a property is really set when doing the update of the doc object in the update process.

[ddresch]

The merge is up-to-date with the latest version incl. V7 updates.