MiniMagick may fail for a variety of reasons, including "the file type
is not allowed in the ImageMagick security policy we use".

Instead of showing a "This file name is restricted. Delete this file
and upload again after changing the name" error message to the end user,
handle the situation gracefully and let the upload proceed without
adding image dimensions.

Solves https://gitlab.ruhr-uni-bochum.de/FDM/rdm-system/antleaf-projectmanagement/-/issues/428



Signed-off-by: Pascal Ernster <pascal.ernster@rub.de>