patch 8.0.1599: no error message when gdb does not support debugger

Problem:    No error message when gdb does not support the terminal debugger.
Solution:   Check for the response to open the Machine Interface.
diff --git a/src/version.c b/src/version.c
index 4c19271..eabf6fb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -767,6 +767,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1599,
+/**/
     1598,
 /**/
     1597,