patch 9.1.0207: No autocommand when writing session file

Problem:  No autocommand when writing session file
Solution: Add SessionWritePost autocommand
          (Colin Kennedy)

fixes: ##14242
closes: #14288

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Colin Kennedy <colinvfx@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/session.c b/src/session.c
index e39ce4d..eea57a2 100644
--- a/src/session.c
+++ b/src/session.c
@@ -1392,6 +1392,8 @@
 #ifdef FEAT_SESSION
     vim_free(viewFile);
 #endif
+
+    apply_autocmds(EVENT_SESSIONWRITEPOST, NULL, NULL, FALSE, curbuf);
 }
 
 #if (defined(FEAT_VIMINFO) || defined(FEAT_SESSION)) || defined(PROTO)