Specify the behaviour when a ScrollTimeline doesn't have an explicitly specified time range, and an animation associated with it has a target effect end of infinity. Fixes issue #10.

Author: theres-waldo

Overview.bs

@@ -494,8 +494,8 @@ The <dfn>effective time range</dfn> of a {{ScrollTimeline}} is calculated as fol
     directly associated with this timeline.
 
     If any animation directly associated with the timeline has a 
-    [=target effect end=] of infinity, the
-    behavior is unspecified.
+    [=target effect end=] of infinity, the [=effective time range=] 
+    is zero.
 
 :   Otherwise,
 ::  The [=effective time range=] is the {{ScrollTimeline}}'s