Improve logic for dealing with negative limits in compute_histogram in log mode

[astrofrog]

Follow up for #1963

[codecov]

Codecov Report

Merging #1970 into master will increase coverage by 0.02%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #1970      +/-   ##
==========================================
+ Coverage   87.46%   87.49%   +0.02%     
==========================================
  Files         244      244              
  Lines       21715    21719       +4     
==========================================
+ Hits        18993    19002       +9     
+ Misses       2722     2717       -5

Impacted Files	Coverage Δ
glue/core/data.py	89.96% <50%> (-0.26%)	⬇️
glue/app/qt/application.py	78.77% <0%> (+0.83%)	⬆️

---

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 9455df0...c9220fe. Read the comment docs.