If a kanban view is grouped on a many2one, records with the field unset
are displayed in a column "Undefined" displayed first.
But the tab in mobile view doesn't respect this, so we can get:
columns: Undefined colA colB
tabs: colA colB Undefined
So we always get always on the wrong column wrong when clicking on a
tab: clicking on colB we get on colA, clicking on Undefined we get on
colB, ...
note: in this commit the "false" tab has been set to a translatable
"Undefined" name.
issue found when working on #21199
Nicolas Lempereur
bed48ad960