patch 8.2.0649: undo problem whn an InsertLeave autocommand resets undo

Problem:    Undo problem whn an InsertLeave autocommand resets undo. (Kutsan
            Kaplan)
Solution:   Do not create a new undo block when leaving Insert mode.
diff --git a/src/edit.c b/src/edit.c
index 05518ce..7f4f765 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -5994,7 +5994,8 @@
 
     // If u_savesub() was called then we are not prepared to start
     // a new line.  Call u_save() with no contents to fix that.
-    if (tick != CHANGEDTICK(curbuf))
+    // Except when leaving Insert mode.
+    if (event != EVENT_INSERTLEAVE && tick != CHANGEDTICK(curbuf))
 	u_save(curwin->w_cursor.lnum, (linenr_T)(curwin->w_cursor.lnum + 1));
 
     return r;