Shannon theorem and zero padding
You'll not experience aliasing – in the end, the IDFT result per definition only contains frequency components that can be represented by the original frequency domain.

If you will, just stop worrying about aliasing: the DFT and inverse DFT are just base change matrices in $\mathbb C^N$, and are invertible.

Aliasing can only happen when something is non-invertible. This is not the case here; so, no problem.

What you might see is leakage, but you're already taking care of that by windowing.