Detect initial commit directly instead of relying on error

[ouuan]

Now it tries the parent commit when the previous blame is not available and relies on the error to detect the initial commit.

https://github.com/FabijanZulj/blame.nvim/blob/314398fec334848d431cc7c87f65baf7e72aa1d1/lua/blame/blame_stack.lua#L292-L294

I'm not sure how this is useful. Can we just show the "no previous commit" info when the previous blame is not available?

BTW, when not using a notification plugin, now the debug error message overrides (hides) the "no previous commit" info:

https://github.com/FabijanZulj/blame.nvim/blob/314398fec334848d431cc7c87f65baf7e72aa1d1/lua/blame/blame_stack.lua#L77-L83