patch 8.0.1848: 'termwinscroll' does not work properly

Problem:    'termwinscroll' does not work properly. (Dominique Pelle)
Solution:   Subtract removed scrollback from the scrollback count.  Add a test
            for 'termwinscroll'. (closes #2909)

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1848,
 /**/
     1847,
 /**/