patch 7.4.1547

Problem:    Getting a cterm highlight attribute that is not set results in the
            string "-1".
Solution:   Return an empty string. (Taro Muraoka)

src/version.c

@@ -743,6 +743,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1547,
 /**/
     1546,
 /**/