Fix hidden posts not disappearing

Resolves [this issue (from reddit)](https://www.reddit.com/r/RESissues/comments/2ps1hp/)

It is only safe to make this assumption if we are fading the element in, which is what the behavior used to be [before refactoring](https://github.com/honestbleeps/Reddit-Enhancement-Suite/blob/634a34f3c5c23f8ab1873a114d5606dabf13eea5/lib/core/utils.js#L629) (notice that this is only present in fadeElementIn, not fadeElementOut).
[](https://github.com/honestbleeps/Reddit-Enhancement-Suite/commit/85dce9030d38bc5f7426d1c2c3046184b613d9f8#diff-9fa41a0df75b0d0555d1c410e214ce0cL622)