improve image caching and disposal

app/lib/domain/services/generic_website.dart

@@ -294,8 +294,10 @@ class GenericWebsiteService extends _$GenericWebsiteService {
   Future<BrowserIcon?> getCachedIcon(Uri url) async {
     if (url.scheme.startsWith('https') || url.scheme.startsWith('http')) {
       final cachedBrowserIcon = _browserIconCache.get(url.origin);
-      if (cachedBrowserIcon != null) {
+      if (cachedBrowserIcon?.image.value != null) {
         return cachedBrowserIcon;
+      } else if (cachedBrowserIcon != null) {
+        _browserIconCache.remove(url.origin);
       }
 
       final cachedIcon = await _cacheRepository.getCachedIcon(url.origin);

app/lib/domain/services/generic_website.g.dart

@@ -42,7 +42,7 @@ final class GenericWebsiteServiceProvider
 }
 
 String _$genericWebsiteServiceHash() =>
-    r'32a561820bda432f3c17e05b9da9c85871efffb4';
+    r'80b0f7113368bdd6fbe43fc27d2ab7332fe4b692';
 
 abstract class _$GenericWebsiteService extends $Notifier<void> {
   void build();