Fix bug #10170 with extra scrolling after C-s.

 src/xdisp.c (try_scrolling): Don't set scroll_down_p if dy is zero.

src/ChangeLog

+2011-12-09  Eli Zaretskii  <eliz@gnu.org>
+
+	* xdisp.c (try_scrolling): Don't set scroll_down_p if dy is zero.
+	(Bug#10170)
+
 2011-12-09  YAMAMOTO Mitsuharu  <mituharu@math.s.chiba-u.ac.jp>
 
 	* unexelf.c (unexec) [NS_IMPL_GNUSTEP]: Take account of the case

src/xdisp.c

@@ -14360,7 +14360,7 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
     {
       int scroll_margin_y;
-      /* Compute the pixel ypos of the scroll margin, then move it to
+      /* Compute the pixel ypos of the scroll margin, then move IT to
 	 either that ypos or PT, whichever comes first.  */
       start_display (&it, w, startp);
       scroll_margin_y = it.last_visible_y - this_scroll_margin
@@ -14390,7 +14390,8 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
 	  if (dy > scroll_max)
 	    return SCROLLING_FAILED;
-	  scroll_down_p = 1;
+	  if (dy > 0)
+	    scroll_down_p = 1;
 	}
     }