Vector store may not have a name

This is not required in the API, so we must account for unnamed ones.

Author: kzu

src/dotnet-openai/Vectors/ListCommand.cs

@@ -45,9 +45,10 @@ public override int Execute(CommandContext context, ListCommandSettings settings
                 foreach (var node in nodes["data"]!.AsArray().AsEnumerable().Where(x => x != null))
                 {
                     var id = node!["id"]!.ToString();
-                    var name = node["name"]!.ToString();
+                    var name = node["name"]?.ToString() ?? "";
 
-                    mapper.SetId(name, id);
+                    if (!string.IsNullOrEmpty(name))
+                        mapper.SetId(name, id);
 
                     table.AddRow(
                         id,