patch 8.1.1749: Coverity warns for using negative index

Problem:    Coverity warns for using negative index.
Solution:   Move using index inside "if".
diff --git a/src/version.c b/src/version.c
index d1dde86..1a65cef 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1749,
+/**/
     1748,
 /**/
     1747,