Trying to split a way at the end node should not throw an error

[AndrewBuck]

Currently if you select one or more nodes along a way and use the split way command (hotkey P), if one of the nodes is at the end of the way to be split, instead of just ignoring that node JOSM throws an error and the operation is aborted. Although obviously no action needs to be taken for that node since it is already split there; throwing an error and especially aborting the action is going to far. JOSM should instead, just ignore this node (preferably silently, but throwing a warning would be ok too) and move on with the rest of the splitting procedure.

I have found at least two common use case scenarios where this crops up and causes user frustration:

1) When splitting out a bridge section in a road by selecting the two end nodes and pressing split (often there is already a split existing at one end of the bridge triggering this issue).

2) When taking the last two nodes of a road that ends in a turning circle and trying to split off a short section to be expanded into a circle with shift+O. I often find myself selecting the two nodes to split them off for some reason and then run into this issue.

[Don-vip]

In 5401/josm:

fix #7918 - Trying to split a way at the end node should not throw an error