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/dedicated_v.cpp

@@ -21,6 +21,7 @@
 #include "../core/random_func.hpp"
 #include "../saveload/saveload.h"
 #include "../thread.h"
+#include "../window_func.h"
 #include "dedicated_v.h"
 
 #ifdef __OS2__
@@ -295,6 +296,7 @@ void VideoDriver_Dedicated::MainLoop()
 			next_tick = cur_ticks + std::chrono::milliseconds(MILLISECONDS_PER_TICK);
 
 			GameLoop();
+			InputLoop();
 			UpdateWindows();
 		}