Fix movement.  Adapted from
https://github.com/egoboo/egoboo/commit/3d4509d2722657c808fd32c93765db2e8597fc9a

Index: src/game/game.c
--- src/game/game.c.orig
+++ src/game/game.c
@@ -2052,8 +2052,10 @@ void set_one_player_latch( const PLA_REF player )
         if (( CAM_TURN_GOOD == PCamera->turn_mode && 1 == local_numlpla ) ||
             !control_is_pressed( INPUT_DEVICE_KEYBOARD, CONTROL_CAMERA ) )
         {
-            joy_pos.x = ( control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_RIGHT ) - control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_LEFT ) );
-            joy_pos.y = ( control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_DOWN ) - control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_UP ) );
+            if ( control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_RIGHT ) ) joy_pos.x++;
+            if ( control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_LEFT )  ) joy_pos.x--;
+            if ( control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_DOWN )  ) joy_pos.y++;
+            if ( control_is_pressed( INPUT_DEVICE_KEYBOARD,  CONTROL_UP )    ) joy_pos.y--;
 
             if ( CAM_TURN_GOOD == PCamera->turn_mode &&
                  1 == local_numlpla )  joy_pos.x = 0;
