patch 8.0.1331: possible crash when window can be zero lines high

Problem:    Possible crash when window can be zero lines high. (Joseph
            Dornisch)
Solution:   Only set w_fraction if the window is at least two lines high.
diff --git a/src/version.c b/src/version.c
index ebc57ed..cda1ef3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1331,
+/**/
     1330,
 /**/
     1329,