patch 8.0.0637: crash when using some version of GTK 3

Problem:    Crash when using some version of GTK 3.
Solution:   Add #ifdefs around incrementing the menu index. (Kazunobu
            Kuriyama)
diff --git a/src/version.c b/src/version.c
index 6d33f12..23653c1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    637,
+/**/
     636,
 /**/
     635,