Added Keybord input filter to only register first key press.

OpenRA.Platforms.Default/Sdl2Input.cs

@@ -161,7 +161,11 @@ namespace OpenRA.Platforms.Default
 								Platform.CurrentPlatform == PlatformType.Windows)
 								Game.Exit();
 							else
+							{
+								// Only register initial key press
+								if (e.key.repeat == 0)
 									inputHandler.OnKeyInput(keyEvent);
+							}
 
 							break;
 						}