[Statistics view] Commits and changes lines are shifted

[n-rodriguez]

Some commits may have no file changes (empty commit, merge, etc).
In result commits line and changes line are shifted because of missing date in series list :

total_commits_by_day.keys :

---
- 2014-04-17
- 2014-04-18
- 2014-04-19
- 2014-04-20
- 2014-04-23
- 2014-04-25
- 2014-04-26
- 2014-06-23
- 2014-09-03
- 2014-09-08
- 2014-09-09
- 2014-09-10
- 2014-09-11
- 2014-09-16
- 2014-09-17
- 2014-09-24
- 2014-09-29
- 2014-11-08
- 2015-01-15
- 2015-01-31
- 2015-02-27
- 2015-03-11
- 2015-03-12
- 2015-03-16

total_changes_by_day.keys :

---
- 2014-04-17
- 2014-04-18
- 2014-04-19
- 2014-04-20
- 2014-04-23
- 2014-04-25
- 2014-04-26
- 2014-06-23
- 2014-09-03
- 2014-09-09
- 2014-09-10
- 2014-09-11
- 2014-09-16
- 2014-09-17
- 2014-09-24
- 2014-09-29
- 2014-11-08
- 2015-01-15
- 2015-01-31
- 2015-02-27
- 2015-03-11
- 2015-03-12
- 2015-03-16

The missing date here is 2014-09-08 in total_changes_by_day.keys.
In total_commits_by_day.keys :

• 2014-09-03
• 2014-09-08
• 2014-09-09

So the commit exists but there are no changes. The entry should exists in total_changes_by_day with a 0 value (no changes).