patch 9.1.0406: Divide by zero with getmousepos() and 'smoothscroll'

Problem:  Divide by zero with getmousepos() and 'smoothscroll'.
Solution: Don't compute skip_lines when width1 is zero.
          (zeertzjq)

closes: #14747

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index cbd2909..e601c82 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    406,
+/**/
     405,
 /**/
     404,