[fractal] room-history: Dont overwrite message row parent's CSS classes

[Kévin Commaille <kcommaille src gnome org>]

commit 852dd054625678114e36937eb5e180c04673017f
Author: Kévin Commaille <zecakeh tedomum fr>
Date:   Sat Aug 20 19:02:28 2022 +0200

    room-history: Dont overwrite message row parent's CSS classes

 src/session/content/room_history/message_row/mod.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/src/session/content/room_history/message_row/mod.rs 
b/src/session/content/room_history/message_row/mod.rs
index 23c2e8c6f..dd1326228 100644
--- a/src/session/content/room_history/message_row/mod.rs
+++ b/src/session/content/room_history/message_row/mod.rs
@@ -138,9 +138,9 @@ impl MessageRow {
         priv_.header.set_visible(visible);
 
         if let Some(list_item) = self.parent().and_then(|w| w.parent()) {
-            if visible {
-                list_item.set_css_classes(&["has-header"]);
-            } else {
+            if visible && !list_item.has_css_class("has-header") {
+                list_item.add_css_class("has-header");
+            } else if !visible && list_item.has_css_class("has-header") {
                 list_item.remove_css_class("has-header");
             }
         }