issue is missing context.region in the execute() after calling
window_manager.fileselect_add() [in the invoke() -- indirectly via
ImportHelper].

Havent hunted down the actual reason / breaking commit but for now do
the following as a bandaid:

• in case of adding multiple images, we can skip ImportHelper all

together and store positions in own invoke(). context.region is still
valid then. no functional change.

• in the case of adding an image sequence, we can refrain from calling

bpy.ops.node.add_node() and place the nodes at the far left [as it was
done before rBA922272e6bed1]

Fixes T59962, T60130