history-search-* and undo lists

[Grisha Levit]

There's some issue with undo list handling in history-search-* commands:

Doing a successful search with a line that has an undo list causes the
undo entries from that list to leaked:

HISTFILE= INPUTRC=/ bash --norc -in <<< $'X\nX\e[5~'
=================================================================
ERROR: LeakSanitizer: detected memory leaks
Direct leak of 32 byte(s) in 1 object(s) allocated from:
     #2 alloc_undo_entry                 undo.c:75:23
     #3 rl_add_undo                      undo.c:92:10
     #4 rl_insert_text                   text.c:114:2
     #5 _rl_insert_char                  text.c:935:7
     #6 rl_insert                        text.c:989:42
     #7 _rl_dispatch_subseq              readline.c:941:8
     #8 _rl_dispatch                     readline.c:876:10
     #9 readline_internal_char           readline.c:690:11
    #10 readline_internal_charloop       readline.c:737:11
    #11 readline_internal                readline.c:749:18
    #12 readline                         readline.c:387:11


...and running the search again causes a use-after-free when accessing
prev_line_found in rl_history_search_internal:

HISTFILE= INPUTRC=/ bash --norc -in <<< $'X\nX\nX\e[5~\e[5~'
=================================================================
ERROR: AddressSanitizer: heap-use-after-free on address 0xe53d8842ae50
READ of size 1 at 0xe53d8842ae50 thread T0
     #0 rl_history_search_internal       search.c:634:30
     #1 rl_history_search_backward       search.c:746:11
     #2 _rl_dispatch_subseq              readline.c:941:8

0xe53d8842ae50 is 0 bytes in 2-byte region [0xe53d8842ae50,0xe53d8842ae52)
freed by thread T0 here:
     #2 _rl_maybe_replace_line           misc.c:344:7
     #3 rl_history_search_internal       search.c:609:3
     #4 rl_history_search_backward       search.c:746:11
     #5 _rl_dispatch_subseq              readline.c:941:8

previously allocated by thread T0 here:
     #2 alloc_history_entry              history.c:296:25
     #3 add_history                      istory.c:428:10
     #4 really_add_history               bashhist.c:963:3
     #5 bash_add_history                 bashhist.c:948:5


...or when using revert-all-newline:

echo 'set revert-all-at-newline on' > i
HISTFILE= INPUTRC=i bash --norc -in <<< $'X\nX\e[5~\exnext-history\nX'
=================================================================
ERROR: AddressSanitizer: heap-use-after-free on address 0xef01e9428830
READ of size 8 at 0xef01e9428830 thread T0
     #0 _rl_free_undo_list               undo.c:106:16
     #1 rl_free_undo_list                undo.c:122:3
     #2 readline_common_teardown         readline.c:507:5
     #3 readline_internal_teardown       readline.c:518:3

0xef01e9428830 is 0 bytes in 32-byte region [0xef01e9428830,0xef01e9428850)
freed by thread T0 here:
     #2 rl_do_undo                       undo.c:267:7
     #3 _rl_revert_previous_lines        misc.c:500:6
     #4 _rl_revert_all_lines             misc.c:530:3
     #5 readline_common_teardown         readline.c:502:5
     #6 readline_internal_teardown       readline.c:518:3

previously allocated by thread T0 here:
     #2 alloc_undo_entry                 undo.c:75:23
     #3 rl_add_undo                      undo.c:92:10
     #4 rl_end_undo_group                undo.c:305:3
     #5 _rl_replace_text                 text.c:205:3
     #6 make_history_line_current        search.c:134:3
     #7 rl_history_search_internal       search.c:667:3
     #8 rl_history_search_backward       search.c:746:11