The previous commit only solves the problem when using the default
theme using factory settings. For previously saved themes, there could
still be problems, as the alpha values were still 0.
This commit improves the logic here so that while keyframe points on
unselected F-Curves will still get faded out (to not stick out too much
from the curves they live on), but the effect will not be as pronounced
(i.e. the points will stay visible all the time).
288bcb2593