patch 8.2.4335: no autocommand event triggered before changing directory

Problem:    No autocommand event triggered before changing directory. (Ronnie
            Magatti)
Solution:   Add DirChangedPre. (closes #9721)
diff --git a/src/misc2.c b/src/misc2.c
index fac836f..38da7e5 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -1914,6 +1914,9 @@
 	// nothing to do
 	return OK;
 
+    if (trigger_autocmd != NULL)
+	trigger_DirChangedPre((char_u *)trigger_autocmd, new_dir);
+
     if (mch_chdir((char *)new_dir) != 0)
 	return FAIL;