patch 7.4.717

Problem:    ":let list += list" can change a locked list.
Solution:   Check for the lock earlier. (Olaf Dabrunz)

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    717,
 /**/
     716,
 /**/