Potential invalid userRating calculation when ratingCount is zero

### 🐛 Describe the bug

## A clear and concise description of what the bug is.

In `explore_story_controller.dart`, the user rating is calculated as:

userData['ratingTotal'] / userData['ratingCount'];

If `ratingCount` is 0 or null, this results in `Infinity` or `NaN` instead of a valid rating value.

Although this does not throw an exception in Dart, it can lead to incorrect or invalid values being displayed in the UI.

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## Sample code to reproduce the problem

Example:

```dart
final ratingTotal = 0;
final ratingCount = 0;

final result = ratingTotal / ratingCount;
print(result); // NaN