Fix error when checking for exclusions

[redmunds]

I noticed this when looking at the JS Code Hints code. If there are no files returned from preferences.getExcludedFiles(), then the jscodehints.defaultExclusions will not get checked.

@dangoor We should get this in for Release 0.41

[dangoor]

I was puzzled by how the defaultExclusions were even working, but it turns out that the bug here is that the defaultExclusions are turned off only if you have a code hints preferences file that expressly has no excluded files, which is likely not too common. That said, the defaultExclusions should always apply, so this is a good catch!