patch 8.2.0158: triggering CompleteDone earlier is not backwards compatible

Problem:    Triggering CompleteDone earlier is not backwards compatible.
            (Daniel Hahler)
Solution:   Add CompleteDonePre instead.
diff --git a/src/autocmd.c b/src/autocmd.c
index 13aa065..dce23b8 100644
--- a/src/autocmd.c
+++ b/src/autocmd.c
@@ -114,6 +114,7 @@
     {"ColorSchemePre",	EVENT_COLORSCHEMEPRE},
     {"CompleteChanged",	EVENT_COMPLETECHANGED},
     {"CompleteDone",	EVENT_COMPLETEDONE},
+    {"CompleteDonePre",	EVENT_COMPLETEDONEPRE},
     {"CursorHold",	EVENT_CURSORHOLD},
     {"CursorHoldI",	EVENT_CURSORHOLDI},
     {"CursorMoved",	EVENT_CURSORMOVED},