[TECHNICAL-SUPPORT] LPS-43148 Logo Editor (image_uploader) generates FileExtensionException

Hey Julio,

Sorry for the misleading comment yesterday... :-( I forgot the fact that the "previewURL" comes from an instance variable not from the form directly, so updating the "previewURL" hidden field of the form is fine.

##### Edification

Never check pulls/codes from mobile without seeing the whole picture (code context). :-)

##### Note

As I can see, you fixed-up some of my commits. Thus, I amended the commit messages in two cases
- lipusz@d06739b & lipusz@8472999

Thanks!