Be more robust and don't explode if start_timestamp is not available.
Be more robust and don't explode if start_timestamp is not available.

This should never happen (action being in running state and having no
start_timestamp), but just in case.

armab/st2,lakshmi-kannan/st2,nzlosh/st2,Plexxi/st2,punalpatel/st2,lakshmi-kannan/st2,StackStorm/st2,tonybaloney/st2,nzlosh/st2,emedvedev/st2,emedvedev/st2,punalpatel/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,armab/st2,pixelrebel/st2,StackStorm/st2,peak6/st2,tonybaloney/st2,Plexxi/st2,tonybaloney/st2,dennybaa/st2,emedvedev/st2,dennybaa/st2,peak6/st2,punalpatel/st2,lakshmi-kannan/st2,Plexxi/st2,pixelrebel/st2,StackStorm/st2,armab/st2,pixelrebel/st2,peak6/st2,dennybaa/st2,nzlosh/st2