Zoom slider bar not properly updated on first start up.

[CapPow]

An example bug report, illustrating an existing problem.

Describe the bug
When the program first starts, the preview window's zoom % and slider position are not accurate. Any adjustments to the slider cause it to be correctly updated.

To Reproduce
Steps to reproduce the behavior:

1. Start the program, set preview window's zoom slider to a value greater than 100%
2. Properly close the program
3. Start the program again
4. Observe the preview window's zoom % and position
5. Alter the zoom slider position slightly to see where it should be

Expected behavior
On start up, the program should display the preview zoomed in at the previous session's settings and accurately report the % zoom value above the slider.

Desktop (please complete the following information):

• Observed in Windows 10, and on Manjaro Linux (from source).

Additional context

• This issue appears related to the setMaxZoom() function needing an updated preview window to correctly calculate the available window geometry.
• Calling updatePreview() function before and after .settings.setMaxZoom() solves the issue but doubles CPU load on all zoom alterations.
• Since the issue is only present at start up, a more frugal solution is preferable.