Bug 565593 crash [@ js_DestroyContext] if JS_NewContext fails in CancelExecution. r=jorendorff

--HG--
extra : rebase_source : a3d5e11c53a042e786560b90c2039f9183329a22

js/src/shell/js.cpp

@@ -3591,9 +3591,10 @@ CancelExecution(JSRuntime *rt)
 #ifdef JS_THREADSAFE
     if (gWorkers) {
         JSContext *cx = JS_NewContext(rt, 8192);
-        if (cx)
+        if (cx) {
             js::workers::terminateAll(cx, gWorkers);
-        JS_DestroyContextNoGC(cx);
+            JS_DestroyContextNoGC(cx);
+        }
     }
 #endif
     JS_TriggerAllOperationCallbacks(rt);