improve error handling

Author: simon-massa

lua/CopilotChat/config/providers.lua

@@ -240,11 +240,18 @@ M.copilot = {
       error(err)
     end
 
-    if response.body.endpoints and response.body.endpoints.api then
+    if response.body and response.body.endpoints and response.body.endpoints.api then
       log.info('get_headers ok, authenticated. Use api endpoint: ' .. response.body.endpoints.api)
       M.endpoints_api = response.body.endpoints.api
     else
-      error('get_headers authenticated, but missing key "endpoints.api". response: ' .. utils.serializeTable(response))
+      log.error(
+        'get_headers authenticated, but missing key "endpoints.api" in server response. response: '
+          .. utils.serializeTable(response)
+      )
+      error(
+        'get_headers authenticated, but missing key "endpoints.api" in server response. Check log for details: '
+          .. MC.config.log_path
+      )
     end
 
     return {