patch 8.1.1111: it is not easy to check for infinity

Problem:    It is not easy to check for infinity.
Solution:   Add isinf(). (Ozaki Kiichi, closes #3787)

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1111,
 /**/
     1110,
 /**/