Improve behaviour when we hit a stack overflow / OOM error

runtime/observatory/lib/src/elements/isolate_summary.html

Index: runtime/observatory/lib/src/elements/isolate_summary.html
diff --git a/runtime/observatory/lib/src/elements/isolate_summary.html b/runtime/observatory/lib/src/elements/isolate_summary.html
index c146bfac194d2c7617960db3d1b624f6d8d73753..d71aa76c0081b7dff302f385a9f9815659a0fe10 100644
--- a/runtime/observatory/lib/src/elements/isolate_summary.html
+++ b/runtime/observatory/lib/src/elements/isolate_summary.html
@@ -64,11 +64,13 @@
         <template if="{{ isolate.pauseEvent.kind == 'PauseException' }}">
           by exception
         </template>
-        at
-        <function-ref ref="{{ isolate.topFrame.function }}">
-        </function-ref>
-        (<source-link location="{{ isolate.topFrame.location }}">
-        </source-link>)
+        <template if="{{ isolate.topFrame != null }}">
+          at
+          <function-ref ref="{{ isolate.topFrame.function }}">
+          </function-ref>
+          (<source-link location="{{ isolate.topFrame.location }}">
+          </source-link>)
+        </template>
       </template>
     </template>