CLSA-2026-1779183235 vim: Fix of 6 CVEs

CVE-2021-4069: copy mlgetcurline in exopen so a flushed line buffer is not used after vimregexec - CVE-2022-2000: truncate IObuff with "..." in appendcommand when remaining space is below threshold - CVE-2022-3099: guard docmdline breakpoint lookup with linesga.galen currentline check -...