Change how long strip side padding works

[WizaHX]

Describe your suggested feature

Change how settings >reader>long strip>side padding works. Currently it behaves as if the padding is part of the picture, so if you zoom in a little - it can wiggle left and right, instead of ignoring the padded part and keep image horizontally centered. I feel like it should behave same as if you zoomed out and then you zoom in before image edge hits the screen bounds, meaning as long as the image width is fully contained in the screen, there shouldn't be left/right wiggle.

Other details

No response

Acknowledgements

• [x] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• [x] I have written a short but informative title.
• [x] I have updated the app to version 0.18.0.
• [x] I will fill out all of the requested information in this form.