Don't check for image on attribute drop on canvas
Don't check for image on attribute drop on canvas

If our drag event doesn't have a file or a URL, don't bother telling the
user about file extensions -- they probably weren't dragging anything but
an attribute.

[#144034943]
concord-consortium/building-models,concord-consortium/building-models,concord-consortium/building-models,concord-consortium/building-models,concord-consortium/building-models