Fix of CVE: CVE-2021-3973, CVE-2021-3974, CVE-2021-4019, CVE-2021-4069, CVE-2021-3984

CVE-2021-3974: fix using freed memory with regexp using a mark - CVE-2021-3984: fix illegal memory access when C-indenting - CVE-2021-3973: fix crash when using CTRL-W f without finding a file name - CVE-2021-4019: fix buffer overflow with long help argument - CVE-2021-4069: fix using freed...