d7053ba030
Regression caused by [0] which changed node selection to use
PRESS for selection and CLICK_DRAG to transform the selection.
This conflicted with Alt-LMB which would select the node then
pass-though to node.background_sample, preventing the drag event
from being activated.
Resolve by only activating background-sample when the cursor
isn't over a node or socket.
[0]: 4c3e91e5f5