bug#47909: doc-id searches only match last record in the file

[Brad Knotwell]

I use:  Editor:      GNU Emacs 27.2 (build 1, x86_64-apple-darwin17.7.0, Carbon 
Version 158 AppKit 1561.6)

        Hyperbole:   7.1.3
        Sys Type:    x86_64-apple-darwin17.7.0
        OS Type:     darwin
        Window Sys:  mac
        News Reader: Gnus v5.13

If you setup a file like what's at the end of the email, setup the
doc-id-indices variable (NB:  the documentation for that variables needs
updating as it says it's a list but it throws an error on a list and
works with a filename passed in as a string), and add two doc-id links
like the following:

[BigBaboonNation-001]
[BigBaboon-001]

Hyperbole will only find the 'BigBaboon-001' entry.  For the
'BigBaboonNation-001' entry, you'll receive the following error:

   Wrong type argument: integer-or-marker-p, nil

If I switch the entry order in the file, the behavior will swap with
'BigBaboonNation-001' matching.

-----------
Title:  Big Baboon Nation        ID: [BigBaboonNation-001]
Email-To: bknotwell@yahoo.com
Distribution:  everywhere

Abstract:  hello world

References:

Author:  b knotwell
Copyright:
Keywords:

Online-Format:
Online-Loc:       
"https://lists.gnu.org/archive/html/bug-hyperbole/2021-04/msg00005.html";
Printed-Format:
Printed-Loc:      Local Library
Printable-Loc:    ""
Source-Format:
Source-Loc:       ""
Date:
Version:
Version-Changes:
------------
Title:  Big Baboon         ID: [BigBaboon-001]
Email-To: bknotwell@yahoo.com
Distribution:  everywhere

Abstract:  hello world

References:

Author:  b knotwell
Copyright:
Keywords:

Online-Format:
Online-Loc:       
"https://lists.gnu.org/archive/html/bug-hyperbole/2021-04/msg00006.html";
Printed-Format:
Printed-Loc:      Local Library
Printable-Loc:    ""
Source-Format:
Source-Loc:       ""
Date:
Version:
Version-Changes: