fontchooser: Fix programmatic selection

The changes in 8caadaf404 did not work
since the selection model is set to autoselect,
so the first time items are added to the list,
we select one.

Fixes: #4564

What this commit does not fix is scrolling the
selected item into view.

gtk/gtkfontchooserwidget.c

@@ -2334,10 +2334,12 @@ gtk_font_chooser_widget_merge_font_desc (GtkFontChooserWidget       *fontchooser
   if (mask & PANGO_FONT_MASK_SIZE)
     {
       double font_size = (double) pango_font_description_get_size (fontchooser->font_desc) / PANGO_SCALE;
-      /* XXX: This clamps, which can cause it to reloop into here, do we need
-       * to block its signal handler? */
+      g_signal_handlers_block_by_func (gtk_range_get_adjustment (GTK_RANGE (fontchooser->size_slider)), size_change_cb, fontchooser);
+      g_signal_handlers_block_by_func (gtk_spin_button_get_adjustment (GTK_SPIN_BUTTON(fontchooser->size_spin)), size_change_cb, fontchooser);
       gtk_range_set_value (GTK_RANGE (fontchooser->size_slider), font_size);
       gtk_spin_button_set_value (GTK_SPIN_BUTTON (fontchooser->size_spin), font_size);
+      g_signal_handlers_unblock_by_func (gtk_range_get_adjustment (GTK_RANGE (fontchooser->size_slider)), size_change_cb, fontchooser);
+      g_signal_handlers_unblock_by_func (gtk_spin_button_get_adjustment (GTK_SPIN_BUTTON(fontchooser->size_spin)), size_change_cb, fontchooser);
     }
   if (mask & (PANGO_FONT_MASK_FAMILY | PANGO_FONT_MASK_STYLE | PANGO_FONT_MASK_VARIANT |
               PANGO_FONT_MASK_WEIGHT | PANGO_FONT_MASK_STRETCH))

gtk/ui/gtkfontchooserwidget.ui

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <interface domain="gtk40">
   <object class="GtkSingleSelection" id="selection">
+    <property name="autoselect">0</property>
     <signal name="notify::selected-item" handler="selection_changed_cb" object="GtkFontChooserWidget" swapped="0"/>
     <signal name="items-changed" handler="rows_changed_cb" object="GtkFontChooserWidget" swapped="1"/>
     <property name="model">