fix: give default init.lua if none provided

lib/mkNeovimPkg.nix

@@ -27,7 +27,7 @@
   extractPlugin = map (p: p.plugin);
 
   customRC = let
-    rc = ({init ? "", ...}: init) runtime;
+    rc = ({init ? ../lua/default_init.lua, ...}: init) runtime;
   in
     deps.textOrContent rc;
 

lua/sloth-flake/init.lua

@@ -69,7 +69,7 @@ function M.is_loaded(name)
 end
 
 function M.setup(config)
-  local post_init = config.post_init or function() end
+  local post_init = config and config.post_init or function() end
 
   M.init_all()
   post_init()