Prevent crash in animated transform lists
https://bugs.webkit.org/show_bug.cgi?id=110704

Reviewed by Abhishek Arya.

Source/WebCore:

This change prevents accessing values off the end of toAtEndOfDuration by adding a check
for this case. Similar checks were added in r116458 but the author failed to catch this
case. WK110706 has been filed to handle this case in general.

This change also makes a trivial change that marks effectiveFrom as const.

Test: svg/animations/animateTransform-list-crash.html

* svg/SVGAnimatedTransformList.cpp:
(WebCore::SVGAnimatedTransformListAnimator::calculateAnimatedValue):

LayoutTests:

* svg/animations/animateTransform-list-crash-expected.txt: Added.
* svg/animations/animateTransform-list-crash.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143859 268f45cc-cd09-0410-ab3c-d52691b4dbfc