add Accounts.is_already_admin? check

lib/memex/accounts.ex

@@ -363,10 +363,16 @@ defmodule Memex.Accounts do
   """
   @spec is_admin?(User.t()) :: boolean()
   def is_admin?(%User{id: user_id}) do
-    Repo.one(from u in User, where: u.id == ^user_id and u.role == :admin)
+    Repo.exists?(from u in User, where: u.id == ^user_id and u.role == :admin)
-    |> is_nil()
   end
 
+  @doc """
+  Checks to see if user has the admin role
+  """
+  @spec is_already_admin?(User.t() | nil) :: boolean()
+  def is_already_admin?(%User{role: :admin}), do: true
+  def is_already_admin?(_invalid_user), do: false
+
   ## Confirmation
 
   @doc """

lib/memex_web/components/topbar.ex

@@ -65,7 +65,7 @@ defmodule MemexWeb.Components.Topbar do
           <li class="mx-2 my-1 border-left border border-primary-700">​</li>
 
           <%= if @current_user do %>
-            <%= if @current_user.role == :admin do %>
+            <%= if @current_user |> Accounts.is_already_admin?() do %>
               <li class="mx-2 my-1">
                 <.link
                   navigate={Routes.invite_index_path(Endpoint, :index)}