[ISSUE] vim-x11: terminal background leaks into vim's

[blehel <blehel@users.noreply.github.com>]

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New issue by blehel on void-packages repository

https://github.com/void-linux/void-packages/issues/23497

Description:
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### System

* xuname:  
  Void 5.4.48_1 x86_64 GenuineIntel notuptodate rrFFFF
* package:  
  vim-x11-8.2.1095_1

### Problem description

After upgrading from 8.2.0891_1 to 8.2.1095_1, in urxvt when opening a file in vim, there are some annoying black spots at the top: 
[example1](https://i.imgur.com/DKbjNnJ.png)
[example2](https://i.imgur.com/esyGF8q.png)
[example3](https://i.imgur.com/8iO0KcR.png)
Previously all of this was the blue color of the background. Pressing CTRL-L to redraw the screen or scrolling down until the affected region goes off-screen does away with the problem.
Note that if I change the terminal background to some other color, that will be the color that creates these spots, so this is about the terminal background not being drawn over.

### Steps to reproduce the behavior

1. Edit your vimrc so that you use a colorscheme with a background different to your terminal's. Mine is a custom one based on `blue`, and my terminal background is black.
So for example add `colorscheme blue` to your vimrc. (setting it from the ex prompt does not bring out the issue).
2. Start `urxvt` (although I've seen similar behaviour - black spots appearing in place of the background color - in the past in terminal emulators which do not support the `bce` /background color erase/ terminal capability, like `kitty`).
3. Open something in vim.

I don't exclude this being an rxvt-unicode problem, but it was the vim upgrade which broke things.