bugfix unhandled ex in case of duplicateexception (#862)

Co-authored-by: Florian Mader <florian.mader@outlook.com>

src/PublicApi/Middleware/ExceptionMiddleware.cs

@@ -41,7 +41,8 @@ public class ExceptionMiddleware
                 Message = duplicationException.Message
             }.ToString());
         }
-
+        else
+        {
             context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
             await context.Response.WriteAsync(new ErrorDetails()
             {
@@ -50,3 +51,4 @@ public class ExceptionMiddleware
             }.ToString());
         }
     }
+}