Build bot fail if previouslly run on unmergable code

Build bot ran on unmergable code in opendnssec #14 - shouldnt have done that.
But it ran and failed and added build 1 as failed on that one commit.
Then the that commit was fixed and the fix was rebase so it became a new commit without status.
When the build bot was run again it failed right of because it couldnt get the status and found build 1 failed.