[fix] fix value_range in HORIZON

[skoudoro]

This PR fix #2243.

Sometimes, the range value of the first dataset volume is empty/null. This is the case with our isbi2013_3shell dataset.
So the goal of this fix is to select the volume with a relevant value range for the HORIZON visualization

[skoudoro]

Can you have a quick check @areeshatariq and @jhlegarreta?

[codecov]

Codecov Report

Merging #2249 into master will decrease coverage by 0.01%.
The diff coverage is 10.00%.

@@            Coverage Diff             @@
##           master    #2249      +/-   ##
==========================================
- Coverage   91.38%   91.36%   -0.02%     
==========================================
  Files         252      252              
  Lines       32933    32941       +8     
  Branches     3462     3465       +3     
==========================================
+ Hits        30095    30097       +2     
- Misses       2079     2085       +6     
  Partials      759      759              

Impacted Files	Coverage Δ
dipy/viz/panel.py	64.16% <10.00%> (-1.46%)	⬇️
dipy/segment/tests/test_bundles.py	89.52% <0.00%> (-0.96%)	⬇️
dipy/viz/app.py	77.47% <0.00%> (+0.49%)	⬆️

[jhlegarreta]

Have not tested locally, but looks a fair solution. Thanks for doing this.

[jhlegarreta]

CI build failures (related to SSL certificates during the package installation steps) are unrelated to this patch set. We trust the passing builds. Merging.