gclient: Don't die on empty .gclient_entries file

Bug: 707313
Change-Id: Ic3860aa6b9aeaba3ec02ab8dac8dd63429f917cc
Reviewed-on: https://chromium-review.googlesource.com/466688
Reviewed-by: Erik Staab <estaab@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

gclient.py

@@ -1309,7 +1309,7 @@ it or fix the checkout.
       exec(gclient_utils.FileRead(filename), scope)
     except SyntaxError as e:
       gclient_utils.SyntaxErrorToError(filename, e)
-    return scope['entries']
+    return scope.get('entries', {})
 
   def _EnforceRevisions(self):
     """Checks for revision overrides."""