Closes #4193 by making the widget in question get cast to a box, rather than a vbox.
Closes #4193 by making the widget in question get cast to a box, rather than a vbox.

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