ImageBase64Formatter tries to render a plain string

Patch #2 fixes this issue, both for the 8.x-1.x-dev branch and the 2.0.x branch.
Assigning it to the 2.0.x branch now, since that's the recommended one, but hopefully this would get fixed in multiple branches.
Also increasing priority, because fatal errors when rendering images is kind of important for a module to render images.

Thanks you very much.

Automatically closed - issue fixed for 2 weeks with no activity.