Fix in_restart causing fatal error while video is shutdown

Connecting to a server running a different fs_game and using a
autoexec.cfg containing in_restart would hit a fatal error in IN_Init().

    IN_Init called before SDL_Init( SDL_INIT_VIDEO )

Reported by smokey2k on the ioquake3 forum.

code/sys/sys_main.c

@@ -112,6 +112,14 @@ Restart the input subsystem
 */
 void Sys_In_Restart_f( void )
 {
+#ifndef DEDICATED
+	if( !SDL_WasInit( SDL_INIT_VIDEO ) )
+	{
+		Com_Printf( "in_restart: Cannot restart input while video is shutdown\n" );
+		return;
+	}
+#endif
+
 	IN_Restart( );
 }