tightvnc: add patches for four CVEs
Security fixes for:
* CVE-2019-8287
* CVE-2019-15678
* CVE-2019-15679
* CVE-2019-15680
mostly adapted from patches fixing similar issues in the actively
maintained libvnc
(#73970)
(cherry picked from commit 2482f8b8dca0f57466d20f9dcf2ff3d5cd16adbf)
