Always refresh a changed scroll value, even if there's no scrollbar

See Textualize#1201.

See
Textualize#1201 (comment)
though -- there has been internal discussion about how there may be a need
to even inhibit by-code scrolling (as opposed to by-input) scrolling, in
some situations. This would likely require that there's something
higher-level, perhaps, that doesn't even attempt to animate `scroll_x` or
`scroll_y` in the first place.

Consider this a placeholder approach for the moment.

src/textual/widget.py

@@ -805,14 +805,14 @@ def watch_hover_style(
     def watch_scroll_x(self, old_value: float, new_value: float) -> None:
         if self.show_horizontal_scrollbar:
             self.horizontal_scrollbar.position = round(new_value)
-            if round(old_value) != round(new_value):
-                self._refresh_scroll()
+        if round(old_value) != round(new_value):
+            self._refresh_scroll()
 
     def watch_scroll_y(self, old_value: float, new_value: float) -> None:
         if self.show_vertical_scrollbar:
             self.vertical_scrollbar.position = round(new_value)
-            if round(old_value) != round(new_value):
-                self._refresh_scroll()
+        if round(old_value) != round(new_value):
+            self._refresh_scroll()
 
     def validate_scroll_x(self, value: float) -> float:
         return clamp(value, 0, self.max_scroll_x)