fixed widget mounting errors

lib/view/pages/absence_report/absence_report_view.dart

@@ -173,7 +173,12 @@ class _AbsenceReportViewState extends State<AbsenceReportView> {
           icon: Icons.error_outline,
           text: errorToUserMessage(snapshot.error),
           button: ElevatedButton.icon(
-              onPressed: () => setState(() => _init = _load()),
+            onPressed: () {
+              final reload = _load();
+              setState(() {
+                _init = reload;
+              });
+            },
             icon: const Icon(Icons.refresh),
             label: const Text('Erneut versuchen'),
           ),

lib/widget/user_avatar.dart

@@ -230,11 +230,15 @@ class _UserAvatarState extends State<UserAvatar> {
 
     final pending = _pendingAvatars.putIfAbsent(url, () {
       final future = _fetch(url);
-      future.whenComplete(() {
+      // Cleanup hangs off an error-neutralised copy: whenComplete on `future`
+      // itself returns a second future that forwards the error unawaited.
+      unawaited(
+        future.then<void>((_) {}, onError: (_) {}).whenComplete(() {
           if (identical(_pendingAvatars[url], future)) {
             _pendingAvatars.remove(url);
           }
-      });
+        }),
+      );
       return future;
     });