🔨 fixes output bug with NULL responses instead of crashing .net

[CakeRepository]

Purpose

Fixes bug where it wouldn't play audio in example .net error
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
at SpeakerOutput.EnqueueForPlayback(BinaryData audioData) in D:\repo\aoai-realtime-audio-sdk\dotnet\samples\console-from-mic\SpeakerOutput.cs:line 29
at Program.Main(String[] args) in D:\repo\aoai-realtime-audio-sdk\dotnet\samples\console-from-mic\Program.cs:line 93
at Program.Main(String[] args) in D:\repo\aoai-realtime-audio-sdk\dotnet\samples\console-from-mic\Program.cs:line 42
at Program.

(String[] args)

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[X] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

• Get the code

git clone https://github.com/CakeRepository/aoai-realtime-audio-sdk.git
cd aoai-realtime-audio-sdk
git checkout Audio-output-issues
npm install

• Test the code

After pull and variables set for system to get Realtime Audio in Azure AI or OpenAI to function properly 
open the cloned directory in admin powershell and navigate cd .\dotnet\samples\console-from-mic\
dotnet run

What to Check

Verify that the following are valid

• Conversation plays to default audio device
• example console output:
  PS D:\repo\aoai-realtime-audio-sdk\dotnet\samples\console-from-mic> dotnet run
• Connecting to Azure OpenAI endpoint (AZURE_OPENAI_ENDPOINT): https://cake-eus2.openai.azure.com/
• Using API key (AZURE_OPENAI_API_KEY): 3wLa6**
• Using deployment (AZURE_OPENAI_DEPLOYMENT): gpt-4o-mini-realtime-preview
  <<< Connected: session started

Listening to microphone input
(Just tell the app you're done to finish)

<<< Start of speech detected @ 00:00:01.4400000
<<< End of speech detected @ 00:00:02.6560000

USER: Hello, how are you?

I'm doing great, thank you! How about you?
<<< Start of speech detected @ 00:00:07.5840000
<<< End of speech detected @ 00:00:08.7680000

USER: Okay, have a good day

Thanks! You have a great day too! If you need anything else, just let me know. Goodbye!

Other Information