fix(inline): last_chat maybe nil, e.g. on first usage

[hulufei]

Description

Run :codecompanion hello after installation got following error:

Error executing Lua callback: ...ects/codecompanion.nvim/lua/codecompanion/utils/util.lua:24: bad argument #1 to 'pairs' (table expect
ed, got nil)
stack traceback:
        [C]: in function 'pairs'
        ...ects/codecompanion.nvim/lua/codecompanion/utils/util.lua:24: in function 'count'
        ...decompanion.nvim/lua/codecompanion/strategies/inline.lua:168: in function 'new'
        ...i/projects/codecompanion.nvim/lua/codecompanion/init.lua:21: in function 'inline'
        ...ojects/codecompanion.nvim/lua/codecompanion/commands.lua:55: in function <...ojects/codecompanion.nvim/lua/codecompanion/co
mmands.lua:21>

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Checklist

• [x] I've read the CONTRIBUTING guidelines.

[hulufei]

Seems solved.