resetting the lambda is wrong for some code paths when performing mdrun -rereun
A typo leading to a logic bug is messing up how the lambda vector is set in when performing -rerun.
Basically, a check for whether delta_lambda is zero goes the wrong way--When delta_lambda is zero, it
does the thing that it's supposed to do when delta_lambda isn't zero.
Fix to be uploaded as soon as I have a redmine issue number.