[Bug]: False "no result" using ffgrep in plain mode

### Which fff frontend?

Neovim plugin (fff.nvim)

### has logs

_No response_

### Description

I'm searching for the sequence "com.github.sabomichal" in my repo (big java monorepo, multiple maven sub-modules) using :FFGrep and it shows no result.
I'm at the root, of the repo, "com.github.sabomichal" is present multiple times in the repo, yet it shows "no result".
When I enable the regex or fuzzy search => now I can see the results.

This is the exacte same string.

This is really a problem because at first I thought that "com.github.sabomichal" was really absent from my repo and removed what I thought was dead code. But it was not.

It may be a consequence of a trade off you choose to improve performances, but the tool not being reliable is a great issue for me.

I found a workaround right now by using the fuzzy mode which seems to not have this issue.

Start by reproducing the report with :FFGrep in plain mode from the repository root, using the literal string "com.github.sabomichal" in a repository containing multiple matches. Compare plain search with regex and fuzzy modes to locate the differing behavior; done means plain mode reliably returns all matching results.

Written by the indexing model from the issue text.