Fix confusing error when no tasks present
Fix confusing error when no tasks present

Fixes #472

When a service doesn't yet exist for a new app, we would return a nasty
error message before. This removes that error message.

That said, this only returns a blank response now.  Not sure if there'd
be something better here.

When an app doesn't exist at all in Empire, we still get an appropriate
error:

```
error: Request failed, the specified resource does not exist
```

zofuthan/empire,iserko/empire,no2key/empire,mhahn/empire,remind101/empire,zhakui/empire,markpeek/empire,mhahn/empire,iserko/empire,vfulco/empire,lihuanghai/empire,mhahn/empire,markpeek/empire,vfulco/empire,remind101/empire,zofuthan/empire,zhakui/empire,no2key/empire,lihuanghai/empire,iserko/empire,remind101/empire