bug#46999: 28.0.50; semantic-idle-summary-mode moves point during eldoc

[nvp]

When `semantic-idle-summary-mode` is active in c-mode and the
cursor is on an empty line, the cursor is moved to the next
non-empty line when `semantic-idle-summary-mode`'s eldoc
function executes. I think this was introduced after commit
2987376bc3 with the introduction of the
`eldoc-documentation-functions` hook.

From emacs -Q
  1. open a buffer in c-mode
  2. enable `semantic-mode`, `eldoc-mode`, and
     `semantic-idle-summary-mode`
  3. Move cursor to empty line, eg. '|' in

    int main(int argc, char *argv[]) {
      |  
      return 0;
    }
  4. Idle momentarily to allow eldoc to run


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20, cairo version 1.16.0)
 of 2021-03-07 built on noah-M51AC
Repository revision: c1f4a16cf3d71aa3f67c1c209e7060dc71afc545
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12009000
System Description: Ubuntu 20.04.2 LTS

Configured using:
 'configure --prefix=/usr/local --with-modules --with-xwidgets'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SOUND
THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM XWIDGETS GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: C/*l

Minor modes in effect:
  global-semanticdb-minor-mode: t
  global-semantic-idle-scheduler-mode: t
  semantic-idle-summary-mode: t
  semantic-idle-scheduler-mode: t
  semantic-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs auth-source password-cache json map text-property-search
time-date subr-x mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils semantic/edit cus-start cus-load
semantic/tag-file cl-extra help-mode semantic/db-file data-debug ring
cedet-files semantic/bovine/c semantic/decorate/include
semantic/decorate/mode semantic/decorate pulse hideif
semantic/bovine/c-by semantic/lex-spp semantic/bovine/gcc semantic/dep
semantic/bovine semantic/analyze/refs semantic/db-find semantic/db-ref
semantic/db-mode semantic/idle semantic/analyze semantic/sort
semantic/scope semantic/analyze/fcn semantic/db eieio-base cl-seq seq
semantic/format ezimage semantic/tag-ls semantic/find semantic/ctxt
semantic/util-modes semantic/util semantic pp semantic/tag semantic/lex
semantic/fw eieio byte-opt bytecomp byte-compile cconv eieio-core
cl-macs gv eieio-loaddefs mode-local find-func cedet cc-mode cc-fonts
cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs
cl-loaddefs cl-lib iso-transl tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode elisp-mode lisp-mode prog-mode register page
tab-bar menu-bar rfn-eshadow isearch easymenu timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core term/tty-colors frame
minibuffer cl-generic cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite charscript charprop case-table epa-hook jka-cmpr-hook help
simple abbrev obarray cl-preloaded nadvice button loaddefs faces
cus-face macroexp files window text-properties overlay sha1 md5 base64
format env code-pages mule custom widget hashtable-print-readable
backquote threads xwidget-internal dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 110450 13191)
 (symbols 48 14119 1)
 (strings 32 36471 2341)
 (string-bytes 1 1299327)
 (vectors 16 21234)
 (vector-slots 8 275385 9904)
 (floats 8 31 340)
 (intervals 56 255 0)
 (buffers 992 12))