bug#51312: 29.0.50; Indenting vectors with leading spaces errors out

[Lars Ingebrigtsen]

Trying to use the newish space-after-parenthesis syntax errors out when
you hit tab on the second line:

[ :foo :zot
      :bar]

forward-sexp: Scan error: "Containing expression ends prematurely", 1, 1



In GNU Emacs 29.0.50 (build 39, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, 
cairo version 1.16.0)
 of 2021-10-20 built on elva
Repository revision: 62591c164cd6d0b0555e11b160ffa81bd3bb010f
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux bookworm/sid

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   bloggy blog: http://lars.ingebrigtsen.no