audioconvert: fix rare unaligned load exceptions
Supposed causes described in the issue. Also improve float semantics.
Fixes #3790 (closed)
Partially reverts d47353c0. It included no description, thus I ask for a review to ensure I didn't regress something important.
Briefly tested on Ryzen 5 4500U with AVX optimized resampler being used.
Edited by Dmitry Sharshakov