patch 8.2.1092: not checking if saving for undo succeeds

Problem:    Not checking if saving for undo succeeds.
Solution:   Bail out if u_savesub() returns FAIL.
diff --git a/src/version.c b/src/version.c
index 82eb990..cac669e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1092,
+/**/
     1091,
 /**/
     1090,