[Command::Spec] Fix crash

Closes https://github.com/CocoaPods/CocoaPods/issues/1543

CHANGELOG.md

@@ -53,6 +53,11 @@ To install or update CocoaPods see this [guide](http://docs.cocoapods.org/guides
   [Ladislav Martincik](https://github.com/martincik)
   [#2482](https://github.com/CocoaPods/CocoaPods/issues/2482)
 
+* Fix crash when the URL of a private GitHub repo is passed to `pod spec
+  create` as an argument.  
+  [Fabio Pelosin](https://github.com/fabiopelosin)
+  [#1543](https://github.com/CocoaPods/CocoaPods/issues/1543)
+
 
 ## 0.34.0.rc2
 

lib/cocoapods/command/spec.rb

@@ -426,7 +426,9 @@ module Pod
 
       def github_data_for_template(repo_id)
         repo = GitHub.repo(repo_id)
+        raise Informative, "Unable to fetch data for `#{repo_id}`" unless repo
         user = GitHub.user(repo['owner']['login'])
+        raise Informative, "Unable to fetch data for `#{repo['owner']['login']}`" unless user
         data = {}
 
         data[:name]          = repo['name']