Bug 1402547 - Add crashtest for multiple empty SMIL values; r=hiro

I have verified that this fails without the code changes from the previous patch
in this series, and passes with them.

MozReview-Commit-ID: 1respvNVQaC

--HG--
extra : rebase_source : 82007792f23465edb1d286b721edeea850e2aaa3

dom/smil/crashtests/1402547-1.html

@@ -0,0 +1,3 @@
+<svg>
+<animate id='a' calcMode='discrete' attributeName='height' by='-159'/>
+<animate id='a' calcMode='discrete' attributeName='height' by='-159'/>

dom/smil/crashtests/crashtests.list

@@ -53,3 +53,4 @@ load 709907-1.svg
 load 720103-1.svg
 load 1010681-1.svg
 load 1375596-1.svg
+load 1402547-1.html