try/catch for malformed uris in showdir code

I was getting this error in my website logs:

```
/root/data/ploy/work/a6a8373b2b72e4d6754edb78c645c5207db960ba.1379261349952/node_modules/ecstatic/lib/ecstatic/showdir.js:105
              + ent.encode(decodeURI(
                           ^
URIError: URI malformed
    at decodeURI (native)
    at writeRow (/root/data/ploy/work/a6a8373b2b72e4d6754edb78c645c5207db960ba.1379261349952/node_modules/ecstatic/lib/ecstatic/showdir.js:105:28)
    at Array.forEach (native)
    at render (/root/data/ploy/work/a6a8373b2b72e4d6754edb78c645c5207db960ba.1379261349952/node_modules/ecstatic/lib/ecstatic/showdir.js:112:61)
    at /root/data/ploy/work/a6a8373b2b72e4d6754edb78c645c5207db960ba.1379261349952/node_modules/ecstatic/lib/ecstatic/showdir.js:55:15
    at Object.oncomplete (fs.js:107:15)
                                  
```

so I wrote a failing test and then stuck a try/catch around the `decodeURI()` call, which makes the test pass.