.Net: Don't allow function name/id to be overwritten with an empty string (#9601)

### Motivation and Context

Closes #9567 

### Description

The fix handles the case where a streaming update contains an empty
string for the function name. I haven't been able to reproduce the
scenario where this happens and I have asked the issue creator for more
information. The function name has a max size of 64 chars and when I use
that the function isn't split over multiple streaming responses.

Referencing the approach shown here:
https://community.openai.com/t/functions-calling-with-streaming/305742

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

Author: markwallace-microsoft

dotnet/src/SemanticKernel.Abstractions/Contents/FunctionCallContentBuilder.cs

@@ -181,13 +181,13 @@ private static void TrackStreamingFunctionCallUpdate(StreamingFunctionCallUpdate
 
         // If we have an call id, ensure the index is being tracked. Even if it's not a function update,
         // we want to keep track of it so we can send back an error.
-        if (update.CallId is string id)
+        if (update.CallId is string id && !string.IsNullOrEmpty(id))
         {
             (functionCallIdsByIndex ??= [])[update.FunctionCallIndex] = id;
         }
 
         // Ensure we're tracking the function's name.
-        if (update.Name is string name)
+        if (update.Name is string name && !string.IsNullOrEmpty(name))
         {
             (functionNamesByIndex ??= [])[update.FunctionCallIndex] = name;
         }

dotnet/src/SemanticKernel.UnitTests/Contents/FunctionCallBuilder/FunctionCallContentBuilderTests.cs

@@ -46,6 +46,41 @@ public void ItShouldBuildFunctionCallContentForOneFunction(JsonSerializerOptions
         Assert.Null(functionCall.Exception);
     }
 
+    [Theory]
+    [ClassData(typeof(TestJsonSerializerOptionsForKernelArguments))]
+    public void ItShouldNotOverwriteFunctionNameOrId(JsonSerializerOptions? jsos)
+    {
+        // Arrange
+        var sut = jsos is not null ? new FunctionCallContentBuilder(jsos) : new FunctionCallContentBuilder();
+
+        // Act
+        var update1 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: "f_101", name: null, arguments: null);
+        sut.Append(update1);
+
+        var update2 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: "WeatherUtils-GetTemperature", arguments: null);
+        sut.Append(update2);
+
+        var update3 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: "", name: "", arguments: "{\"city\":");
+        sut.Append(update3);
+
+        var update4 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: null, arguments: "\"Seattle\"}");
+        sut.Append(update4);
+
+        var functionCalls = sut.Build();
+
+        // Assert
+        var functionCall = Assert.Single(functionCalls);
+
+        Assert.Equal("f_101", functionCall.Id);
+        Assert.Equal("WeatherUtils", functionCall.PluginName);
+        Assert.Equal("GetTemperature", functionCall.FunctionName);
+
+        Assert.NotNull(functionCall.Arguments);
+        Assert.Equal("Seattle", functionCall.Arguments["city"]);
+
+        Assert.Null(functionCall.Exception);
+    }
+
     [Theory]
     [ClassData(typeof(TestJsonSerializerOptionsForKernelArguments))]
     public void ItShouldBuildFunctionCallContentForManyFunctions(JsonSerializerOptions? jsos)