patch 9.0.1561: display wrong when moving cursor to above the top line

Problem:    Display wrong when moving cursor to above the top line and
            'smoothscroll' is set.
Solution:   Call adjust_skipcol() in more places and make it work better.
            (Luuk van Baal, closes #12395)

src/textobject.c

@@ -472,6 +472,7 @@ bck_word(long count, int bigword, int stop)
 finished:
 	stop = FALSE;
     }
+    adjust_skipcol();
     return OK;
 }
 
@@ -598,6 +599,7 @@ bckend_word(
 		return OK;
 	}
     }
+    adjust_skipcol();
     return OK;
 }