clicking and dragging toolbars/sidebars duplicates last icon in a different way

[luzpaz]

This is slightly different than #31 so I opened a new ticket:
To reproduce:

1. Click and hold on the left toolbar in an empty space (not on a icon)
2. While the mouse button is still depressed move the mouse upwards towards the icon above it
   Result:
   On the left toolbar: the above icon will be a duplicate of the icon that you're moving
   On the right toolbar: you'll see the same phenomena as the left toolbar + the first icon at the top of the toolbar disappears.
   See gif

[luzpaz]

Refinement: the left toolbar example is just showing us the bug when there are only 2 icons in the toolbar. If there are more that 2 you see the effect that happens in the right toolbar.

[nitramr]

Should be fixed in 9fe9da3. I've added a flag which starts dragging only if mouse was pressed over a tab.

[luzpaz]

Confirmed fix on 9fe9da3
Nice job @nitramr 👍