Mouse wheel up in page mode starts two pages down after xreader window focus regained

 * Xreader version 2.4.4 (xreader --version)
 * Distribution - (Mint 19.3)

Issue

When looking at the PDF in page mode, clicking on another opened window, clicking back to xreader window and trying to scroll up with the mouse wheel, the PDF is positioned two pages down before it starts decrementing pages (since I want to move up the PDF file). After two wheell scrolls the initial page is reached (the one I was looking at before the xreader focus was lost) and after third scroll the desired page is reached.

Steps to reproduce

Open PDF file (I tried several).
Go into page mode view (non-continuous / best fit Ctrl+2).
Scroll down to arbitrary page (i.e. 10).
Open a web browser or any other app to switch to (in order for xreader to lose focus). Actually just moving mouse cursor off the xreader window is enough.
Click back on the xreader window toolbar or document itself (or just start scrolling).
Observe the page number/page content of the PDF.
It will start at page 12, go through page 11 and reach page 10 after two scroll up.
After third wheel scroll the page I wanted (page 9) is reached.

Expected behaviour

Open PDF file (I tried several).
Go into page mode view (non-continuous / best fit Ctrl+2).
Scroll down to arbitrary page (i.e. 10).
Open a web browser or any other app to switch to (in order for xreader to lose focus).
Click back on the xreader window toolbar or document itself (or just start scrolling).
Observe the page number/page content of the PDF.
It should start at page 10, and reach page 9 after one scroll up.

Other information

With the test case steps being the same, this is also observed:

• Not using page view mode does not exhibit the same behavior.
• Scrolling down with the mouse wheel does not exhibit the same behavior.
• Using keyboard up key does not exhibit the same behavior.

Reproduce the issue in Xreader 2.4.4 on Mint 19.3 using Ctrl+2 for page mode, then switch focus and scroll upward. Start by tracing Xreader's page-mode mouse-wheel handling around focus regain; no source file or test is named in the issue. Done means the same page remains selected after focus returns and one upward scroll moves from page 10 to page 9.