fix: terminal buffer previews not initially scrolled

[rjooske]

Description

When you preview a terminal buffer for the first time after :Telescope buffers, the preview is not scrolled to and centered to the line the cursor is on, unlike normal buffers that have a file associated with them.
This PR fixes the issue so that the preview for a terminal buffer is correctly scrolled.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Steps to reproduce the issue

1. Start neovim
2. Create a terminal buffer (:terminal) and inside it, run seq 1000 (or something else that produces lots of lines)
3. Open a random file
4. Run :Telescope buffers

• The first time you preview the terminal buffer, the preview is not scrolled to the line the cursor is on.
• Preview the other entry (the file you opened) and preview the terminal buffer again. Now the preview is correctly scrolled.
• After this PR is applied, the preview is correctly scrolled from the first time on.

Configuration:

• Neovim version (nvim --version):

NVIM v0.9.5
Build type: Release
LuaJIT 2.1.1692716794

• Operating system and version: Ubuntu 22.04 (inside docker container)

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[jamestrew]

Thanks. The steps to reproduce was very helpful too :)