Do not abort on error in changelog.py

15:07:13 [Drive-beta] Running shell script
15:07:13 + tools/release.sh --create release
15:07:14 >>> [release 4.0.2] Generating the changelog
15:07:14 >>> Changelog.py v1.2.8
15:07:14 >>> Retrieving latest created tag
15:07:14 >>> Retrieving commits
15:07:14 >>> Retrieving issues
15:07:14 >>> Fetching informations of NXDRIVE-1347
15:07:14 Traceback (most recent call last):
15:07:14   File "tools/changelog.py", line 314, in <module>
15:07:14     exit(main())
15:07:14   File "tools/changelog.py", line 310, in main
15:07:14     changelog([issue for issue in get_issues(args)], formatter=args.format)
15:07:14   File "tools/changelog.py", line 173, in get_issues
15:07:14     data = get_issue_infos(commit)
15:07:14   File "tools/changelog.py", line 188, in get_issue_infos
15:07:14     data = content.json()
15:07:14   File "/usr/lib/python2.7/dist-packages/requests/models.py", line 892, in json
15:07:14     return complexjson.loads(self.text, **kwargs)
15:07:14   File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
15:07:14     return _default_decoder.decode(s)
15:07:14   File "/usr/lib/python2.7/json/decoder.py", line 364, in decode
15:07:14     obj, end = self.raw_decode(s, idx=_w(s, 0).end())
15:07:14   File "/usr/lib/python2.7/json/decoder.py", line 382, in raw_decode
15:07:14     raise ValueError("No JSON object could be decoded")
15:07:14 ValueError: No JSON object could be decoded