CVE-2023-48234: in nv_zet() (normal.c), reject digit input that would
overflow the count accumulator by checking
n > (LONG_MAX - (nchar - "0")) / 10 before n = n * 10 + (nchar - "0"),
so a large normal-mode z count no longer wraps around in long
arithmetic; equivalent to upstream commits 58f9befca1 and 22cbc8a4e1
combined.
CVE-2022-3705: in qf_update_buffer() (quickfix.c), guard the
qf_fill_buffer() call with a minimal backport of the upstream
quickfix_busy mechanism (from upstream 8.1.0488) so that
filetype/BufReadPost/BufWinEnter autocmds fired while filling the
buffer cannot free the location-list qf_info_T out from under us;
equivalent to upstream commit d0fab10ed2 (patch 9.0.0805).