neon: Fix flashing when starting app

packages/neon/neon/lib/src/app.dart

@@ -312,19 +312,24 @@ class _NeonAppState extends State<NeonApp> with WidgetsBindingObserver, tray.Tra
             option: widget.globalOptions.themeOLEDAsDark,
             builder: (final context, final themeOLEDAsDark) => OptionBuilder(
               option: widget.globalOptions.themeKeepOriginalAccentColor,
-              builder: (final context, final themeKeepOriginalAccentColor) => MaterialApp(
+              builder: (final context, final themeKeepOriginalAccentColor) {
+                if (themeMode == null || !platformBrightnessSnapshot.hasData || themeOLEDAsDark == null) {
+                  return Container();
+                }
+                return MaterialApp(
                   localizationsDelegates: AppLocalizations.localizationsDelegates,
                   supportedLocales: AppLocalizations.supportedLocales,
                   navigatorKey: _navigatorKey,
                   theme: getThemeFromNextcloudTheme(
                     _nextcloudTheme,
-                  themeMode ?? ThemeMode.system,
+                    themeMode,
-                  platformBrightnessSnapshot.data ?? Brightness.light,
+                    platformBrightnessSnapshot.data!,
-                  oledAsDark: themeOLEDAsDark ?? false,
+                    oledAsDark: themeOLEDAsDark,
                     keepOriginalAccentColor: _nextcloudTheme == null || (themeKeepOriginalAccentColor ?? false),
                   ),
                   home: Container(),
-              ),
+                );
+              },
             ),
           ),
         ),