Possible NPE in AetherUtils.getRepositoriesAsList()

```
java.lang.NullPointerException
    at ru.qatools.clay.aether.internal.AetherUtils.getRepositoriesAsList(AetherUtils.java:151)
    at ru.qatools.clay.aether.Aether.<init>(Aether.java:59)
    at ru.qatools.clay.aether.Aether.aether(Aether.java:73)
        at my crappy code :)
```

Seems `for (Repository repository : profile.getRepositories()) {` profile may be null.
