Add: draw the screen at a steady pace, also during fast-forward

During fast-forward, the game was drawing as fast as it could. This
means that the fast-forward was limited also by how fast we could
draw, something that people in general don't expect.

To give an extreme case, if you are fully zoomed out on a busy
map, fast-forward would be mostly limited because of the time it
takes to draw the screen.

By decoupling the draw-tick and game-tick, we can keep the pace
of the draw-tick the same while speeding up the game-tick. To use
the extreme case as example again, if you are fully zoomed out
now, the screen only redraws 33.33 times per second, fast-forwarding
or not. This means fast-forward is much more likely to go at the
same speed, no matter what you are looking at.

src/video/null_v.cpp

@@ -10,6 +10,7 @@
 #include "../stdafx.h"
 #include "../gfx_func.h"
 #include "../blitter/factory.hpp"
+#include "../window_func.h"
 #include "null_v.h"
 
 #include "../safeguards.h"
@@ -48,6 +49,7 @@ void VideoDriver_Null::MainLoop()
 
 	for (i = 0; i < this->ticks; i++) {
 		GameLoop();
+		InputLoop();
 		UpdateWindows();
 	}
 }