Prevent crash in createInstanceTimesFromSyncbase

LayoutTests/svg/animations/smil-syncbase-self-dependency.svg

+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" onload="loaded()">
+    <!-- Test whether SMILElement animation self dependencies handled correctly. -->
+    <rect id="rectID" width="100" height="100" fill="green">
+        <animate id="selfID" attributeName="x" begin="0s; selfID.end" dur="0.02s" from="0" to="400"/>
+    </rect>
+    <text id="label" y="150"/>
+    <script>
+        if (window.testRunner) {
+            testRunner.dumpAsText();
+            testRunner.waitUntilDone();
+        }
+
+        function displayMessage() {
+            document.getElementById("label").textContent = "SMILElement animation time self-dependency is" +
+                ((document.getElementById("rectID").x.animVal.value > 0) ? " " : " not ") + "handled.";
+        }
+
+        function loaded() {
+            setTimeout('displayMessage()', 30);
+            if (window.testRunner) {
+                setTimeout('testRunner.notifyDone()', 40);
+            }
+        }
+    </script>
+</svg>