patch 9.0.1602: stray character visible if marker on top of double-wide char

Problem:    Stray character is visible if 'smoothscroll' marker is displayed
            on top of a double-wide character.
Solution:   When overwriting a double-width character with the 'smoothscroll'
            marker clear the second half. (closes #12469)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1602,
 /**/
     1601,
 /**/