Gutter shadow is incorrect with `draw_centered`

[jason5122]

Description of the bug

When using draw_centered, the gutter shadow that appears when scrolling horizontally sometimes appears incorrectly. I believe the degree of incorrectness depends on the length of the text, but I haven't looked into it too much. I found a way to reproduce it reliably on my computer with just the Preferences pane and I've noted it below.

Here's an image of the issue:

Steps to reproduce

1. Start ST in Safe Mode.
2. Open Preferences and set draw_centered to true.
3. In the Preferences split pane, scroll the left window horizontally enough so that the gutter shadow appears.
4. The shadow should now appear incorrectly.

Expected behavior

If the above steps are repeated without draw_centered, the gutter shadow should look normal.

Actual behavior

The gutter shadow appears incorrectly, as seen in the image above.

Sublime Text build number

4134

Operating system & version

macOS 12.4

(Linux) Desktop environment and/or window manager

No response

Additional information

No response

OpenGL context information

No response