[core] Increase default shared memory to 2048 MiB

This should still be reasonable for most machines people are going to run games on,
and means no manual increases are required for every game it has been previously
needed for.

legendary/core.py

@@ -811,7 +811,7 @@ def prepare_download(self, game: Game, base_game: Game = None, base_path: str =
         self.log.debug(f'Using base URL: {base_url}')
 
         if not max_shm:
-            max_shm = self.lgd.config.getint('Legendary', 'max_memory', fallback=1024)
+            max_shm = self.lgd.config.getint('Legendary', 'max_memory', fallback=2048)
 
         if dl_optimizations or is_opt_enabled(game.app_name, new_manifest.meta.build_version):
             self.log.info('Download order optimizations are enabled.')