Input is momentarily unresponsive after unknown button press

[pcen]

After clicking on a unit button that is not implemented, the game is momentarily unresponsive to keyboard input.

Observed on: intel macbook pro

Steps to reproduce:

• start a new game
• try moving a unit with the GoTo button
• immediately after clicking somewhere on the map, rapidly press an arrow key to move the unit via arrow key instead
• unit will not move for ~half a second

Expected behaviour:

• unit should move immediately after pressing an arrow key

This is probably a more widespread issue than just unit movement in which UI freezes under certain scenarios.