patch 7.4.1664

Problem:    Crash in :cgetexpr.
Solution:   Check for NULL pointer. (Dominique) Add a test.

src/version.c

@@ -748,6 +748,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1664,
 /**/
     1663,
 /**/