github_deploy_key: make sure variable exists before use (#10857)

Make sure variable exists before use.

changelogs/fragments/10857-github_deploy_key-err.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "github_deploy_key - fix bug during error handling if no body was present in the result (https://github.com/ansible-collections/community.general/issues/10853, https://github.com/ansible-collections/community.general/pull/10857)."

plugins/modules/github_deploy_key.py

@@ -284,6 +284,8 @@ class GithubDeployKey(object):
         body = info.get('body')
         if body:
             err = self.module.from_json(body)['message']
+        else:
+            err = None
 
         if status_code == 401:
             self.module.fail_json(msg="Failed to connect to {0} due to invalid credentials".format(self.github_url), http_status_code=status_code, error=err)