gnome: support changes to GtkScaleButton on older gtk+

Gtk+3.10 had a different layout of the GtkScaleButton internals.

Refs #77698

Change-Id: Ia8ba50682aa51681f1aedcef37799e3943c6f269
diff --git a/src/currentcallview.cpp b/src/currentcallview.cpp
index 0c21a31..1a8b704 100644
--- a/src/currentcallview.cpp
+++ b/src/currentcallview.cpp
@@ -176,10 +176,14 @@
     GtkScale *scale = NULL;
     GtkWidget *dock = gtk_scale_button_get_popup(button);
 
-    // the dock is a popup window which contains a frame, which contains a box
+    // the dock is a popover which contains a box
     // which contains the + button, scale, and - button
     // we want to get the scale
     if (GtkWidget *box = gtk_bin_get_child(GTK_BIN(dock))) {
+        if (GTK_IS_FRAME(box)) {
+            // support older versions of gtk; the box used to be in a frame
+            box = gtk_bin_get_child(GTK_BIN(box));
+        }
         GList *children = gtk_container_get_children(GTK_CONTAINER(box));
         for (GList *c = children; c && !scale; c = c->next) {
             if (GTK_IS_SCALE(c->data))