patch 8.2.3539: GTK3: with 'rightleft' set scrollbar may move unintentionally

Problem:    GTK3: with 'rightleft' set scrollbar may move unintentionally.
Solution:   Ignore events while moving the scrollbar thumb. (closes #8958)

src/gui_gtk.c

@@ -1011,6 +1011,9 @@ gui_mch_set_scrollbar_thumb(scrollbar_T *sb, long val, long size, long max)
     {
 	GtkAdjustment *adjustment;
 
+	// ignore events triggered by moving the thumb (happens in GTK 3)
+	++hold_gui_events;
+
 	adjustment = gtk_range_get_adjustment(GTK_RANGE(sb->id));
 
 	gtk_adjustment_set_lower(adjustment, 0.0);
@@ -1023,6 +1026,8 @@ gui_mch_set_scrollbar_thumb(scrollbar_T *sb, long val, long size, long max)
 
 	g_signal_handler_block(G_OBJECT(adjustment), (gulong)sb->handler_id);
 
+	--hold_gui_events;
+
 #if !GTK_CHECK_VERSION(3,18,0)
 	gtk_adjustment_changed(adjustment);
 #endif

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3539,
 /**/
     3538,
 /**/