Fix dragndrop upload
Fix dragndrop upload

See #1867. Fixes #202.

(cherry picked from commit d658c64)

Salandora/OctoPrint,Salandora/OctoPrint,JackGavin13/octoprint-test-not-finished,foosel/OctoPrint,Jaesin/OctoPrint,beeverycreative/BEEweb,Jaesin/OctoPrint,Jaesin/OctoPrint,JackGavin13/octoprint-test-not-finished,foosel/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,Salandora/OctoPrint,JackGavin13/octoprint-test-not-finished,beeverycreative/BEEweb,Salandora/OctoPrint,beeverycreative/BEEweb,foosel/OctoPrint,beeverycreative/BEEweb,JackGavin13/octoprint-test-not-finished