Forbid interactive resize operation if tile doesn't support it

If a window is tiled to the left half of the screen and user attempts to resize the window by dragging its left edge, the tiling state can break.

There are two ways how we could handle this - either untile the window or forbid resizing the window/tile by dragging an edge that's fixed.

This patch implements the second option because it's the easiest one and it's reasonable.