M-x move-to-prev-xref seems to cross node boundaries, which may not be intended

[aidan]

Hello Texinfo maintainers,

Thank you for your work on Texinfo.

I believe I may have found a bug:

*Version:*

info (GNU texinfo) 7.2

*Environment:*

6.19.6-arch1-1

*Steps to reproduce:*

*1. run stand-alone info reader: `*info "(texinfo)Output Formats"*`*

*2. press shift+tab (or M-x *move-to-prev-xref*)*

*Expected behavior:*

The node "(info-stnd)Selecting Xrefs" says:

        <TAB> (‘move-to-next-xref’)
             Move the cursor to the start of the next nearest menu item or
note
             reference in this node.  You can then use <RET>
             (‘select-reference-this-line’) to select the menu or note
             reference.

        ‘M-<TAB>’ (‘move-to-prev-xref’)
        ‘BackTab’
             Move the cursor the start of the nearest previous menu item or
note
             reference in this node.

             The ‘BackTab’ key can be produced on some terminals with
             ‘Shift-<TAB>’.

so both move-to-next-xref and move-to-prev-xref should not cross node
boundaries. While move-to-next-xref behaves as expected, move-to-prev-xref
can cross into a previous node

move-to-prev-xref should do nothing in this case

*Actual behavior:*

The cursor moves to a previous node, on "(standards)Change Logs"