The memory leak happens because `ED_node_link_insert` (called after the
transform operation) overwrites the pre-existing `snode->runtime->iofsd`,
losing the reference without freeing the memory.
So to "move" the reference from `snode->runtime->iofsd` to
`op->customdata`, so that each operator works with its own data.
Reviewed By: Severin
Differential Revision: https://developer.blender.org/D15948
4e4daa6417