Fix SaveColorMap test failure

The commit discretize_color added a line in the Color Map Editor panel,
and it seems that now a scroll bar appears in some cases, so a mouse click
from the test was incorrectly positionned.

Change-Id: I818beb351ae8a16a57cde7c075b6518238f2429c
Merge topic 'discretize_color' into next

1d0e3553 Fix SaveColorMap test failure