#200 node selection with SHIFT KEY is buggy

[Mj Mendoza IV]

scenario: when selecting one node at a time via SHIFT KEY, the first selected node/s moves to upper-left of the stage

to replicate:

1. draw rectangle
2. use Node tool
3. select one corner of rectangle
4. shift-select second corner of rectangle (any corner)

expectation: you select the nodes just fine

currently, you the first node moves to upper left of stage then selects the second node

[Mj Mendoza IV]

Fixed in https://sourceforge.net/p/kage/code/818/