[csharp][generichost] Concatenation can produce invalid url

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/csharp/generichost/latest/NullTypes/src/Org.OpenAPITools/Api/DefaultApi.cs, line 236:

<comment>Path concatenation can produce a double-slash when BaseAddress.AbsolutePath ends with '/', resulting in a different URL path (e.g., /api//widgets/{id}) that may not match server routes.</comment>

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@@ -0,0 +1,383 @@
+                    uriBuilderLocalVar.Scheme = HttpClient.BaseAddress.Scheme;
+                    uriBuilderLocalVar.Path = HttpClient.BaseAddress.AbsolutePath == "/"
+                        ? "/widgets/{id}"
+                        : string.Concat(HttpClient.BaseAddress.AbsolutePath, "/widgets/{id}");
+                    uriBuilderLocalVar.Path = uriBuilderLocalVar.Path.Replace("%7Bid%7D", Uri.EscapeDataString(id.ToString()));
+
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