Bug 371694 - Protect ourselves against null values. r=dveditz

caps/src/nsScriptSecurityManager.cpp

@@ -813,13 +813,13 @@ nsScriptSecurityManager::CheckPropertyAccessImpl(PRUint32 aAction,
     {
         nsCOMPtr<nsIXPConnectWrappedNative> wrapper;
         nsCOMPtr<nsIInterfaceInfo> interfaceInfo;
-        const nsIID* objIID;
+        const nsIID* objIID = nsnull;
         rv = aCallContext->GetCalleeWrapper(getter_AddRefs(wrapper));
-        if (NS_SUCCEEDED(rv))
+        if (NS_SUCCEEDED(rv) && wrapper)
             rv = wrapper->FindInterfaceWithMember(aProperty, getter_AddRefs(interfaceInfo));
-        if (NS_SUCCEEDED(rv))
+        if (NS_SUCCEEDED(rv) && interfaceInfo)
             rv = interfaceInfo->GetIIDShared(&objIID);
-        if (NS_SUCCEEDED(rv))
+        if (NS_SUCCEEDED(rv) && objIID)
         {
             switch (aAction)
             {