Protect against null contexts. bug 340602, r+sr=roc

content/base/src/nsContentUtils.cpp

@@ -2247,6 +2247,10 @@ IsContextOnStack(nsIJSContextStack *aStack, JSContext *aContext)
     rv = iterator->Prev(&ctx);
     NS_ASSERTION(NS_SUCCEEDED(rv), "Broken iterator implementation");
 
+    if (!ctx) {
+      continue;
+    }
+
     if (nsJSUtils::GetDynamicScriptContext(ctx) && ctx == aContext)
       return PR_TRUE;
   }

dom/src/base/nsLocation.cpp

@@ -88,6 +88,11 @@ GetContextFromStack(nsIJSContextStack *aStack, JSContext **aContext)
     rv = iterator->Prev(aContext);
     NS_ASSERTION(NS_SUCCEEDED(rv), "Broken iterator implementation");
 
+    // Consider a null context the end of the line.
+    if (!*aContext) {
+      break;
+    }
+
     if (nsJSUtils::GetDynamicScriptContext(*aContext)) {
       return NS_OK;
     }