Fix incorrect logic around updating service components

Got a traceback when changing my gmail password where `comp` was `None`. Rewrote the tail end of this function to be more correct.

Here's a link to the [whitespace-less diff](https://github.com/mikedougherty/digsby/commit/c80172e8c3079a4a215b76bca5f0bb48ab371de0?w=1)

@stelminator