patch 9.0.1091: assignment to non-existing member causes a crash

Problem:    Assignment to non-existing member causes a crash. (Yegappan
            Lakshmanan)
Solution:   Give an error message and bail out when a member cannot be found.
diff --git a/src/version.c b/src/version.c
index d07e657..5679588 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1091,
+/**/
     1090,
 /**/
     1089,