Fix potential null value issue in MergeDefaultConfig

[lanyeeee]

I installed SKonsole using the following command

dotnet tool install --global SKonsole

However, when I attempted to check the SKonsole version using skonsole --version, I encountered an issue. The error message I received is as follows:

PS D:\Project> skonsole --version
Unhandled exception. System.TypeInitializationException: The type initializer for 'SKonsole.ConfigurationProvider' threw an exception.
 ---> System.Collections.Generic.KeyNotFoundException: The given key 'OPENAI_CHAT_MODEL_ID' was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at SKonsole.ConfigurationProvider.MergeDefaultConfig() in D:\repos\skonsole\apps\SKonsole\ConfigurationProvider.cs:line 41
   at SKonsole.ConfigurationProvider..ctor() in D:\repos\skonsole\apps\SKonsole\ConfigurationProvider.cs:line 27
   at SKonsole.ConfigurationProvider..cctor() in D:\repos\skonsole\apps\SKonsole\ConfigurationProvider.cs:line 9
   --- End of inner exception stack trace ---
   at Program.<Main>$(String[] args) in D:\repos\skonsole\apps\SKonsole\Program.cs:line 9
   at Program.<Main>(String[] args)

To resolve this issue, I cloned the source code, identified the problem, and implemented the necessary fix.
After making the fix, SKonsole worked perfectly.

[lemillermicrosoft]

Thank you! LGTM.