Fix memory leak with drag & drop on 2D viewport
Fix memory leak with drag & drop on 2D viewport

(cherry picked from commit a7d492eb53489083181682839c6d7f83a888ad46)

pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1