[repo-assist] fix: skip empty Cookie header when no cookie parameters are present (#454)

* fix: skip empty Cookie header when no cookie parameters are present

When an API operation has no cookie parameters (the common case),
OperationCompiler was always prepending ("Cookie", "") to the headers
list. fillHeaders only filters null values — not empty strings — so
the empty Cookie: header was sent with every request.

Fix: only prepend the Cookie header when cookieHeader is non-empty.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* ci: trigger checks

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Sergey Tihon <sergey.tihon@gmail.com>

Author: 3 people

src/SwaggerProvider.DesignTime/OperationCompiler.fs

@@ -365,7 +365,10 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
                                         |> Seq.map(fun (name, value) -> $"{name}={value}")
                                         |> String.concat ";"
 
-                                    ("Cookie", cookieHeader) :: (%headers)
+                                    if String.IsNullOrEmpty cookieHeader then
+                                        %headers
+                                    else
+                                        ("Cookie", cookieHeader) :: (%headers)
                                 @>
 
                             (path, queryParams, headers')