patch 8.1.2044: no easy way to process postponed work

Problem:    No easy way to process postponed work. (Paul Jolly)
Solution:   Add the SafeState autocommand event.

src/autocmd.c

@@ -155,6 +155,7 @@ static struct event_name
     {"QuickFixCmdPre",	EVENT_QUICKFIXCMDPRE},
     {"QuitPre",		EVENT_QUITPRE},
     {"RemoteReply",	EVENT_REMOTEREPLY},
+    {"SafeState",	EVENT_SAFESTATE},
     {"SessionLoadPost",	EVENT_SESSIONLOADPOST},
     {"ShellCmdPost",	EVENT_SHELLCMDPOST},
     {"ShellFilterPost",	EVENT_SHELLFILTERPOST},