WebViewer: Drag+Drop of materials with image dependencies does not work

[kwokcb]

Issue

If you drag-drop a MTLX file with image dependencies the image dependencies cannot be found to be bound.
Seems to be the case for

1. Image files in same folder as MTLX file
2. Image files in sub-folders of MTLX file
3. Image files in sibling or parent folders

Perhaps this is due to the usage of relative file paths, though would think that 1 would work.

Diagnosis

Found while loading and examining the console log in a browser.