Ignore BadValue errors from XQueryKeymap

Not sure why I'm getting an error related to the XShape extension from `XQueryKeymap` on my VNC server (only occurs after `slop` has started drawing stuff).  This fixes #15, see related discussion there.

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Mostly for my own future reference, [this table](http://www.rahul.net/kenton/xproto/xrequests.html) lists `QueryKeymap = 44`, and from [this page](http://www.x.org/wiki/Development/Documentation/Protocol/OpCodes/):

```
$ DISPLAY=:1 xdpyinfo -queryExt | grep 'opcode: 128'
    SHAPE  (opcode: 128, base event: 64)
```