patch 8.1.0935: old regexp engine may use invalid buffer

Problem:    Old regexp engine may use invalid buffer for 'iskeyword' or
            uninitialized buffer pointer. (Kuang-che Wu)
Solution:   Set rex.reg_buf when compiling the pattern. (closes #3972)
diff --git a/src/version.c b/src/version.c
index dbf4083..8dd86f0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -780,6 +780,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    935,
+/**/
     934,
 /**/
     933,