patch 8.2.1801: undo file not found when using ":args" or ":next"

Problem:    Undo file not found when using ":args" or ":next".
Solution:   Handle like editing another file. (closes #7072)
diff --git a/src/version.c b/src/version.c
index d784589..80b9319 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1801,
+/**/
     1800,
 /**/
     1799,