Fix JS crashing if initial-state is not set (#2193)

Fixes issues with the JS for at least sign-up pages not working

app/javascript/flavours/glitch/initial_state.js

@@ -96,11 +96,13 @@ const element = document.getElementById('initial-state');
 const initialState = element?.textContent && JSON.parse(element.textContent);
 
 // Glitch-soc-specific “local settings”
+if (initialState) {
   try {
     initialState.local_settings = JSON.parse(localStorage.getItem('mastodon-settings'));
   } catch (e) {
     initialState.local_settings = {};
   }
+}
 
 /**
  * @template {keyof InitialStateMeta} K