Fix legend doesn't get printed in QGIS 2.6

Hi @timlinux, this PR will fix the issue we have in QGIS 2.6 that the legend doesnt get printed. However, opening the impact result on the composer (Open Composer option) is still crashing QGIS 2.6. I have updated my QGIS 2.6 to the latest version (ebfa6000fd49c7d82af9b23f621ca26863393a74). I will look around using simple script if this is an upstream problem.