[rbp] Avoid resizing 1080p fanart

Currently all re-encoded jpgs are resized to multiples of 16 widths and heights.
This causes additional blurring, especially for 1080p (which becomes 1088), as well as subtle aspect ratio errors.

Remove the alignment clamping, and fix up the heights/strides where needed
Merge pull request #3969 from popcornmix/resize_align

[rbp] Avoid resizing 1080p fanart