fix: provider must be set (#868)

lua/avante/providers/init.lua

@@ -161,6 +161,8 @@ end
 ---@param opts {refresh: boolean, provider: AvanteProviderFunctor}
 ---@private
 E.setup = function(opts)
+  opts.provider.setup()
+
   local var = opts.provider.api_key_name
 
   if var == nil or var == "" then
@@ -168,8 +170,6 @@ E.setup = function(opts)
     return
   end
 
-  opts.provider.setup()
-
   -- check if var is a all caps string
   if type(var) == "table" or var:match("^cmd:(.*)") then return end