Make dashed border-style work correctly

There’s a short-path done for focus rectangles, but it can be taken in other conditions, and then fail occasionally to render a dashed line if the border-width is too big.

gtk/gtkrenderborder.c

@@ -405,8 +405,8 @@ set_stroke_style (cairo_t        *cr,
        */
       if (n == nearbyint (n))
         {
-          segments[0] = 1;
-          segments[1] = 2;
+          segments[0] = line_width;
+          segments[1] = 2 * line_width;
         }
       else
         {