Cursor offset when typing

Describe the bug
The further I type on a line the more the cursor is offset away from the text (to the right).

To Reproduce
Detailed steps to reproduce the behavior:

1. Run mvim --clean
2. Type i and start typing.

Expected behavior

The last letter being typed in the screenshot is the period but the cursor is way off.

Screenshots
If applicable, copy/paste the text or add screenshots to help explain your problem.

Environment (please complete the following information):

• Vim version: VIM - Vi IMproved 8.1 (2018 May 18, compiled Oct 21 2019 08:38:12) macOS version Included patches: 1-2168 Compiled by Homebrew
• OS: macOS 10.15
• Terminal: GUI

首先，在 macOS 上使用 mvim --clean 重现该问题，使用所述的 Vim 8.1 环境，并逐步输入更长的行。检查 MacVim GUI 中光标和文本渲染的入口点；完成的标准是输入时光标始终与最后一个字符对齐。