updated for version 7.4.645

Problem:    When splitting the window in a BufAdd autocommand while still in
            the first, empty buffer the window count is wrong.
Solution:   Do not reset b_nwindows to zero and don't increment it.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    645,
 /**/
     644,
 /**/