patch 7.4.1704

Problem:    Using freed memory with "wincmd p". (Dominique Pelle)
Solution:   Also clear "prevwin" in other tab pages.

src/version.c

@@ -748,6 +748,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1704,
 /**/
     1703,
 /**/