Entry: Only open emoji picker on 2ndary icon click

We hijack the secondary icon for the emoji picker, but the handler for
::icon-press did not check the pressed icon and opened it for either.

https://bugzilla.gnome.org/show_bug.cgi?id=786938

gtk/gtkentry.c

@@ -9858,7 +9858,8 @@ pick_emoji (GtkEntry *entry,
             GdkEvent *event,
             gpointer  data)
 {
-  gtk_entry_choose_emoji (entry);
+  if (icon == GTK_ENTRY_ICON_SECONDARY)
+    gtk_entry_choose_emoji (entry);
 }
 
 static void