fix: openfoodfacts#1697 - checking hasError instead of hasData in Fut…

…ureBuilder

Impacted file:
* `loading_dialog.dart`: checking hasError instead of hasData - hasData is not reliable as data can be void or null.

packages/smooth_app/lib/generic_lib/loading_dialog.dart

@@ -93,19 +93,22 @@ class LoadingDialog<T> {
       body: FutureBuilder<T>(
         future: future,
         builder: (BuildContext context, AsyncSnapshot<T> snapshot) {
-          if (snapshot.hasData) {
+          if (snapshot.connectionState == ConnectionState.done) {
+            // Now it's either hasError or successful.
+            // We cannot check hasData because data can be null or void.
+            if (snapshot.hasError) {
+              return ListTile(
+                title: Text(appLocalizations!.error_occurred),
+              );
+            }
             _popDialog(context, snapshot.data);
+            // whatever, anyway we've just pop'ed
             return Container();
-          } else if (snapshot.hasError) {
-            return ListTile(
-              title: Text(appLocalizations!.error_occurred),
-            );
-          } else {
-            return ListTile(
-              leading: const CircularProgressIndicator(),
-              title: Text(title),
-            );
           }
+          return ListTile(
+            leading: const CircularProgressIndicator(),
+            title: Text(title),
+          );
         },
       ),
       actions: <SmoothActionButton>[