This fixes #3253 by checking whether a publishing service is available to handle the selected type of media, and if none can, instead of throwing an exception, it now sends up a dialog.
This fixes #3253 by checking whether a publishing service is available to handle the selected type of media, and if none can, instead of throwing an exception, it now sends up a dialog.


Sanva/shotwell-gsoc,jof/shotwell,jof/shotwell,damianmoore/shotwell,jof/shotwell,h4ck3rm1k3/shotwell,ritchiewilson/shotwell,h4ck3rm1k3/shotwell,abrauchli/shotwell,polymeris/shotwell,jimbonator/shotwell,jimbonator/shotwell,damianmoore/shotwell,Sanva/shotwell-gsoc,polymeris/shotwell,polymeris/shotwell,ritchiewilson/shotwell,ritchiewilson/shotwell,damianmoore/shotwell,jimbonator/shotwell,Sanva/shotwell-gsoc,h4ck3rm1k3/shotwell,abrauchli/shotwell,abrauchli/shotwell