patch 8.2.1091: no check if opening a pty works

Problem:    No check if opening a pty works.
Solution:   Check for invalid file descriptor.
diff --git a/src/version.c b/src/version.c
index e4d8694..82eb990 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1091,
+/**/
     1090,
 /**/
     1089,