fix(file-panel): guard update_components against nil render_data

[dlyongemallo]

Fixes #74.

Relates to sindrets#303.

[Copilot]

Pull request overview

Guards FilePanel:update_components() against being called before the panel buffer is initialized (e.g., when file_panel.show=false), and adds functional coverage for the “panel never opened” lifecycle to ensure these calls don’t error.

Changes:

• Add an early-return guard in FilePanel:update_components() when self.render_data is nil.
• Add functional tests covering FilePanel methods when the panel has not been opened/initialized, plus toggling on/off behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lua/diffview/scene/views/diff/file_panel.lua	Adds a nil-guard so update_components() is safe when the panel hasn’t initialized its buffer/render state.
lua/diffview/tests/functional/panel_spec.lua	Adds functional tests for the show=false lifecycle to prevent regressions around uninitialized panel state.

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