From https://ftp.gnu.org/gnu/bash/bash-5.0-patches/bash50-012

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

			     BASH PATCH REPORT
			     =================

Bash-Release:	5.0
Patch-ID:	bash50-012

Bug-Reported-by:	lessbug@qq.com
Bug-Reference-ID:	<tencent_6AA531D9A5CC4121D86BD5CDA2E0DA98C605@qq.com>
Bug-Reference-URL:

Bug-Description:

When using previous-history to go back beyond the beginning of the history list,
it's possible to move to an incorrect partial line.

Patch (apply with `patch -p0'):

*** ../bash-5.0-patched/lib/readline/misc.c	2017-07-07 17:30:12.000000000 -0400
--- b/lib/readline/misc.c	2019-05-16 11:43:46.000000000 -0400
***************
*** 577,580 ****
--- 590,594 ----
  {
    HIST_ENTRY *old_temp, *temp;
+   int had_saved_line;
  
    if (count < 0)
***************
*** 589,592 ****
--- 603,607 ----
  
    /* If we don't have a line saved, then save this one. */
+   had_saved_line = _rl_saved_line_for_history != 0;
    rl_maybe_save_line ();
  
***************
*** 612,616 ****
    if (temp == 0)
      {
!       rl_maybe_unsave_line ();
        rl_ding ();
      }
--- 627,632 ----
    if (temp == 0)
      {
!       if (had_saved_line == 0)
!         _rl_free_saved_history_line ();
        rl_ding ();
      }
*** ../bash-5.0/patchlevel.h	2016-06-22 14:51:03.000000000 -0400
--- b/patchlevel.h	2016-10-01 11:01:28.000000000 -0400
***************
*** 26,30 ****
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 11
  
  #endif /* _PATCHLEVEL_H_ */
--- 26,30 ----
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 12
  
  #endif /* _PATCHLEVEL_H_ */