acq stream: don't try to compute 1D spectrum with a 1px long line

Line which has both start and end at the same point is not valid.
driver andorcam2: fix sync acquisition

standard acquisition has been updated, but not the sync acquisition, causing sometimes
failures. Now the two function should be synchronized again.
acq stream: improve estimated time for sync acqusition

It used to be far too pesimistic. There is no reason the readout has 60 ms
overhead all the time.

Now we end up being a bit optimistic.
Estimating the overhead without actually trying is really hard.

The change is mostly noticeable on large repetitions with small exposure time.
acq drift: fix anchor region being of the wrong size

after the update on the scale, the resolution ended up being wrong, causing
lots of problems.

Also use a nicer way to ensure we get the latest data from the SEM.