Fix issue when completing the first command in a script with an empty array expression

[MartinGC94]

PR Summary

Fixes tab completion in scenarios like: get-chi<Tab> @()

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[iSazonov]

Fixes tab completion in scenarios like: get-chi<Tab> @()

This works for me without the change.

[MartinGC94]

Fixes tab completion in scenarios like: get-chi<Tab> @()

This works for me without the change.

Which version are you on? I believe this issue was added with my index expression completion changes and I think they only got added in the most recent 7.3.0 preview 8 release.
This issue occurs if you are tab completing a command that starts in the very first position of a script that also contains an empty array expression. The empty array expression creates an empty script extent which has the same starting position as a command in the first position would have. If there's any whitespace before the command then it works properly.

-Edit: You can easily test it here with these 2 lines:
TabExpansion2 -inputScript 'get- @()' -cursorColumn 1
TabExpansion2 -inputScript ' get- @()' -cursorColumn 2
(Note the leading whitespace in the second example)

[ghost]

This pull request has been automatically marked as Review Needed because it has been there has not been any activity for 7 days.
Maintainer, please provide feedback and/or mark it as Waiting on Author

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[daxian-dbw]

LGTM

[daxian-dbw]

To maintainers: according to #18355 (comment), this PR fixes a regression that was introduced in 7.3.0 preview 8. So, we may want to backport this fix to 7.3.0.

[TravisEz13]

/backport to release/v7.3.1

[ghost]

🎉v7.3.1 has been released which incorporates this pull request.:tada:

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