patch 9.0.1607: screenpos() returns wrong row with diff filler lines

Problem:    screenpos() returns wrong row with diff filler lines.
Solution:   Only add filler lines when appropriate.  Also don't add the
            'smoothscroll' marker when w_skipcol is zero. (closes #12485,
            closes #12484)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1607,
 /**/
     1606,
 /**/