tasks/lalinference.py: do not input start time too close to sample time when reading statevector
This fixes https://emfollow.ligo.caltech.edu/sentry/gwcelery/issues/276/?query=is:unresolved
What happened was the following. After one ifo's statevector is read, start
is forced to be the sample time of statevector and that becomes input start time when next ifo's statevector is read. But Inputting the exact sample time causes problems due to numerical errors.
cc: @leo-singer @vivien