Fix deme.size_at(deme.start_time).

[grahamgower]

Closes #427.

[codecov]

Codecov Report

Merging #428 (7b0299c) into main (a34be5c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #428   +/-   ##
=======================================
  Coverage   99.80%   99.80%           
=======================================
  Files           5        5           
  Lines        1552     1554    +2     
=======================================
+ Hits         1549     1551    +2     
  Misses          3        3           

Impacted Files	Coverage Δ
demes/demes.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a34be5c...7b0299c. Read the comment docs.

[jeromekelleher]

Seems like a good approach. Let's see if @molpopgen and @apragsdale agree.

[apragsdale]

Looks good. That’s pretty much exactly what I had in mind. Thanks Graham! Let’s also see what @molpopgen thinks. He might be busy the next day or two it sounds like, but would probably want to have a look.

[molpopgen]

I'll be back at work next Tuesday or Wednesday.

[molpopgen]

This looks good to me! Sorry for the slow reply.