fix: [VIDECO-11489] Subscriber Screen is empty on Android

[Mike-Zhylevych]

This pull request improves the robustness of stream lookup and subscription logic in the OTRNSubscriber class. The main change is the introduction of a dedicated method to find a stream by its ID, searching both subscriber and publisher streams, and updating the logic in onAttachedToWindow to use this method with additional null checks.

Stream lookup and subscription improvements:

• Added a new findStream method to search for a stream by ID in both subscriber streams and publisher streams, making the lookup more comprehensive and reliable.
• Updated the onAttachedToWindow method to use the new findStream method, added null checks for sessionId and streamId, and ensured that subscription only occurs when both session and stream are found.

Contributing checklist

• Code must follow existing styling conventions
• Added a descriptive commit message
• Sample apps updated if needed

Solves issue(s)