Fix warning in matplotlib rendering.

See warning at bottom of:
http://open.cdash.org/viewBuildError.php?type=1&onlydeltap&buildid=2741779

Change-Id: Ib094e2f0d7a8ae6c3a591aadcb853222c598c40f
Minor code lisibility improvements on HTG and HTG geom filter.

Change-Id: I96a5f7fcdbf041e6322699437efd3517d43b01d8
Merge topic 'FixWarning' into master

322fb5e9 Fix warning in matplotlib rendering.
Merge topic 'MinorsCorrectionsOnHTG' into master

c2b36387 Minor code lisibility improvements on HTG and HTG geom filter.