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.

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1092,
 /**/
     1091,
 /**/