layoutsNodesChange() fix with neg values

[adumesny]

Description

• updating higher column layout can cause negative values in layoutsNodesChange()

Steps:

1. load into 3 column, size down to 2 column

2. move item 1 to the right

3. size item 0 to 1 column -> makes item 1 move to top causing layout[3] to have negative values y=-1 and apparently not fixed later when going back to 3 column (TBD)

   let grid = GridStack.init({
   cellHeight: 80,
   columnOpts: {
   layout: "compact",
   breakpoints: [{w:700, c:2},{w:850, c:3}]
   },
   children: [{x: 0, y: 0, w:2, content: '0'}, {x: 2, y: 0, content: '1'}]})

Checklist

• Created tests which fail without the change (if possible)
• All tests passing (yarn test)
• Extended the README / documentation, if necessary